Adhesive bonding composition and electronic components prepared from the same

ABSTRACT

A curable resin or adhesive composition includes at least one monomer, a photoinitiator capable of initiating polymerization of the monomer when exposed to light, and at least one energy converting material, preferably a phosphor, capable of producing light when exposed to radiation (typically X-rays). The material is particularly suitable for bonding components at ambient temperature in situations where the bond joint is not accessible to an external light source. An associated method includes: placing a polymerizable adhesive composition, including a photoinitiator and energy converting material, such as a down-converting phosphor, in contact with at least two components to be bonded to form an assembly; and, irradiating the assembly with radiation at a first wavelength, capable of conversion (down-conversion by the phosphor) to a second wavelength capable of activating the photoinitiator, to prepare items such as inkjet cartridges, wafer-to-wafer assemblies, semiconductors, integrated circuits, and the like.

REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. Ser. No. 16/262,060,filed Jan. 18, 2019, now allowed, the entire contents of which areincorporated herein by reference, which is a Continuation of U.S. Ser.No. 15/459,907, filed Mar. 15, 2017, now U.S. Pat. No. 10,283,476, theentire contents of which are incorporated herein by reference. Thepresent application is related to PCT application no. PCT/US2018/022669,filed Mar. 15, 2018, the entire contents of which are incorporatedherein by reference. The present application is also related to U.S.application Ser. No. 15/455,573, filed Mar. 10, 2017; U.S. applicationSer. No. 15/382,835, filed Dec. 19, 2016; U.S. application Ser. No.14/593,049, filed Jan. 9, 2015; U.S. application Ser. No. 13/102,277,filed May 6, 2011, now U.S. Pat. No. 9,023,249; U.S. Provisionalapplication Ser. No. 61/331,990, filed May 6, 2010, and U.S. Provisionalapplication Ser. No. 61/443,019, filed Feb. 15, 2011, the entirecontents of each of which are hereby incorporated by reference. Thepresent application is also related to U.S. provisional patentapplication 61/161,328, filed Mar. 18, 2009; U.S. provisional patentapplication 61/259,940, filed Nov. 10, 2009; U.S. ProvisionalApplication Ser. No. 60/954,263, filed Aug. 6, 2007, and 61/030,437,filed Feb. 21, 2008; U.S. application Ser. No. 12/059,484, filed Mar.31, 2008; U.S. application Ser. No. 11/935,655, filed Nov. 6, 2007; U.S.Provisional Application Ser. No. 61/042,561, filed Apr. 4, 2008;61/035,559, filed Mar. 11, 2008; and 61/080,140, filed Jul. 11, 2008;U.S. patent application Ser. No. 12/401,478 filed Mar. 10, 2009; U.S.patent application Ser. No. 11/935,655, filed Nov. 6, 2007; U.S. patentapplication Ser. No. 12/059,484, filed Mar. 31, 2008; U.S. patentapplication Ser. No. 12/389,946, filed Feb. 20, 2009; and U.S. patentapplication Ser. No. 12/417,779, filed Apr. 3, 2009, the entire contentsof each of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of Invention

The invention pertains to materials and methods for polymer curing,particularly adhesive curing and bonding, and more particularly tocertain electronic and semiconductor components containing the adhesive,and methods for producing the electronic and semiconductor componentsusing energy conversion and photoinitiator chemistries in applicationswhere access to an external light source is not available and/or wherebonding without a coefficient of thermal expansion mismatch isdesirable.

Discussion of the Background

Thermosetting polymers and adhesives are well known and are used for awide variety of applications. One particularly important applicationdomain is in the field of microelectronics assembly, where thermosetadhesives are used to bond bare die to substrate, establish conductivecontacts, and perform various roles in packaging and sealing structuressuch as glob-top and die-underfill structures. Commercially availablematerials are formulated to meet various requirements, and in additionto the monomer(s) may contain particulate fillers such as metal, oxides,or dielectric powders, as well as various additives to control thermalconductivity, viscosity and other properties. The materials aretypically dispensed as a thixotropic fluid in precise locations, andafter all the parts are placed, the entire assembly is heated to atemperature necessary to polymerize the monomers or crosslink resins.

As modern electronic components evolve to smaller sizes, and integratedcircuits include ever-smaller features such as ultra-shallow junctions,the permissible thermal budget during assembly continues to decrease.New memory device technologies, for example, incorporate phase-changematerials that are temperature sensitive and may need to be assembledusing low-temperature processing. Similarly, polymer composites used fordental restorations must be cured without subjecting the patient to highcuring temperatures. To address these issues, many photo-curing polymersystems have been developed. In general, these systems employ at leastone photoinitiator, which, when exposed to UV light, releases chemicalenergy to form free radicals or cations to initiate the reaction of themonomers at substantially ambient temperatures.

The clear limitation of conventional photoinitiators is the need to havedirect line-of-sight access to a suitable light source. This preventsthe use of conventional materials for advanced processes such asmultilayer stacks of individual silicon dies, because there is no way toget the UV light into the interior of the stack.

Furthermore, the conventional UV curable adhesives cure from the outsidesurface of an adhesive bead to the inside of the adhesive bead; and, inmost cases curing is accompanied by the formation of a skin. In thepresent invention curing is more controllable and can proceed across theentire volume of the adhesive bead.

SUMMARY OF THE INVENTION

One object of the present invention is to provide polymer formulations(i.e. monomers, photoinitiators, and energy converters) that can becured by indirect photoinitiation, i.e. in the absence of line-of-sightaccess to the external energy source.

A further object of the present invention is to provide an adhesivecomposition that may be cured at ambient temperature.

Another object of the present invention is to provide a flowableadhesive composition containing a photoinitiator and an energyconverter, preferably a downconverter such as a phosphor or scintillatormaterial (or a combination of a phosphor and a scintillator material).

Another object of the present invention is to provide a flexible sheetadhesive material capable of being polymerized by selected ionizingradiation.

Another object of the present invention is to provide a method foradhesive bonding at ambient temperature, as well as a method of adhesivebonding suitable for bonding silicon dies or wafers in a stack atambient temperature, along with a wide variety of other enduses.

Another object of the present invention is to provide electronic and/orsemiconductor components containing the adhesive composition of thepresent invention.

These and other objects and advantages of the invention, either alone orin combinations thereof, have been satisfied by the discovery of acurable adhesive composition comprising:

a polymerizable or crosslinkable organic vehicle comprising at least onepolymerizable monomer or a plurality of crosslinkable polymer chains;

at least one photo-initiator responsive to a selected wavelength oflight; and,

at least one energy converting material selected to emit said wavelengthof light when exposed to a selected imparted radiation;

and its use in preparation of various assemblies and constructions,particularly various electronic and semiconductor components.

BRIEF DESCRIPTION OF THE FIGURES

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1 provides an emission spectrum of a material that emits in the UVAregime, upon irradiation with X-rays.

FIG. 2 provides an emission spectrum of a material that emits in the UVBregime, upon irradiation with X-rays.

FIG. 3 provides an emission spectrum of a material that emits in theUVA, UVB, and visible regimes, upon irradiation with X-rays.

FIG. 4 provides emission spectra of two separate materials, CaWO₄ andYaTO₄, upon irradiation with X-rays.

FIG. 5 provides an emission spectrum of a mixture of CaWO₄ and YaTO₄,upon irradiation with X-rays.

FIG. 6 provides emission spectra of a mixture of CaWO₄ and YaTO₄, uponirradiation with X-rays at intensities of 50, 90, and 130 kvp.

FIG. 7 provides a representation of the effects of a large coatingthickness or coating shape on packing factor of a phosphor.

FIG. 8 provides the changes in attenuation of intensity of X-ray betweena phosphor that has a coating and an innate phosphor surface.

FIG. 9 provides a representation of an embodiment of a dam-and-fillapplication of the present invention.

FIG. 10 provides a representation of an embodiment of the presentinvention using an insertion molded piece placed in the substrate tointensify the UV output.

FIGS. 11A and 11B show a representation of a bare silica carrierparticle and a silica carrier particle decorated with nano-size phosphorparticles, respectively.

FIG. 12 provides a representation of a silica carrier particle coatedwith quantum dots or alloyed quantum dots or metal alloys exhibitingplasmonic behavior under X-ray.

FIG. 13 provides a representation of a silica carrier particle decoratedwith nano-sized downconverters and then coated with silica.

FIG. 14 provides a representation of a photoinitiator tethered oradsorbed on the surface of a nano-sized phosphor particle.

FIGS. 15A and 15B provide representations of a silica micro particledecorated with nano-size phosphor particles having photoinitiatorstethered or adsorbed on the surfaces thereof and photoinitiatorstethered directly on a silica coating around a particle that isdecorated with nano-sized phosphors, respectively.

FIGS. 16A and 16B provide representations of a double layered decorationthat is non-tethered with photoinitiators and a double layereddecoration with tethered photoinitiators, respectively.

FIG. 17 provides a representation of an embodiment of an anisotropicconductive polymer sphere of the present invention.

FIG. 18 provides a representation of an embodiment of an anisotropicconductive polymer sphere of the present invention after compression andflattening.

FIG. 19 provides a representation of an embodiment of the presentinvention using anisotropic conductive polymer spheres in an integratedcircuit application, wherein the representation has features exaggeratedfor emphasis.

FIG. 20 provides a representation of a further embodiment of ananisotropic conductive UV emitting polymer sphere of the presentinvention.

FIG. 21 provides a representation of an embodiment of the anisotropicconductive UV emitting polymer sphere of FIG. 20 after compression andflattening.

FIG. 22 provides a representation of an embodiment of the presentinvention using anisotropic conductive UV emitting polymer spheres in anintegrated circuit application, wherein the representation has featuresexaggerated for emphasis.

FIG. 23 provides a representation of a further embodiment of the presentinvention using anisotropic conductive UV emitting polymer spheres.

FIGS. 24A-C provide representations of an embodiment of an X-ray alignerand bonder according to the present invention.

FIGS. 25A-C provide representations of a further embodiment of an X-rayaligner and bonder according to the present invention.

FIGS. 26A-C provide representations of another embodiment of an X-rayaligner and bonder according to the present invention.

FIG. 27 provides a representation of an embodiment of a stationarydispense system having computer control and the ability to program UVintensity and UV source with ON/OFF time.

FIG. 28 provides a representation of a further embodiment of anautomatic dispenser having a mechanical drive system and computercontrol, particularly useful for UV flashing.

FIG. 29 provides a representation of another embodiment of an automaticdispenser having a mechanical drive system with computer control and aheated platen with vacuum apertures.

FIGS. 30A-D provide representations of an embodiment of the presentinvention whereby a screen printer is used for application of theadhesive composition and UV flashing is used to effect a partial cureprior to application of the second substrate and irradiation withX-rays.

FIGS. 31A-C provide representations of an embodiment of the presentinvention bonding a PET component to a cross-ply carbon compositecomponent.

FIG. 32 provides a representation of an embodiment of the presentinvention whereby fillets having direct line-of-sight are further curedby direct application of UV energy.

FIGS. 33A-C provide representations of an embodiment of the presentinvention whereby the 2 adhesives are administered either throughseparate dispensers (FIG. 33A) or through 2 coaxial dispensers (FIGS.33B-C).

FIG. 34 provides a representation of one embodiment of X-ray system foruse in the present invention having automated doors and an internal UVlamp.

FIGS. 35A and 35B provide representations of embodiments of conveyorsystems for use in the present invention.

FIG. 36 provides a representation of an embodiment of the presentinvention using more than one X-ray source for curing of differentassemblies at the same time.

FIGS. 37A-C provide representations of different embodiments of themethod of the present invention whereby the workpiece being irradiatedis oriented in different ways with respect to the radiation source.

FIGS. 38A and 38B provide representations of an embodiment of thepresent invention of a wafer bonding tool having a rotating table androtating arm.

FIG. 39 provides a representation of an embodiment of a die to waferbonding tool that can be used in the present invention.

FIGS. 40A-C provide representations of different embodiments of X-raysystems and conveyor systems useful in the present invention.

FIG. 41 provides a representation of an embodiment of a contactlesschamber design useful in the present invention.

FIG. 42 provides a representation of a further embodiment of acontactless chamber design useful in the present invention.

FIGS. 43A-B provide representations of embodiments of the presentinvention for bonding fasteners to a composite panel.

FIG. 44 provides a representation of use of an embodiment of the presentinvention for production of an underfill assembly.

FIG. 45 provides a representation of use of an embodiment of the presentinvention for production of an underfill on a high density circuit.

FIG. 46 provides a representation of use of an embodiment of the presentinvention for production of a no-flow underfill assembly.

FIG. 47 provides a representation of use of an embodiment of the presentinvention for glob top encapsulation.

FIG. 48 provides a representation of use of an embodiment of the presentinvention as a dam-and-fill adhesive.

FIG. 49 provides a representation of use of an embodiment of the presentinvention in encapsulation through molding.

FIGS. 50A and 50B provide representations of use of embodiments of thepresent invention for lid sealing of logic devices and MEMS devices,respectively.

FIG. 51 provides a representation of use of an embodiment of the presentinvention in glob top encapsulation of a micro ball grid array.

FIG. 52 provides a representation of use of an embodiment of the presentinvention in encapsulation of TAB bond areas between a flex circuit andan integrated circuit (IC).

FIG. 53 provides a representation of use of an embodiment of the presentinvention in bonding of plastic devices having mirror image featuresusing a film adhesive.

FIGS. 54A and 54B provide representations of use of an embodiment of thepresent invention in formation of subassemblies having fluidic channels.

FIGS. 55A and 55B provide representations of use of an embodiment of thepresent invention in connecting an active device to a fluidic reservoir.

FIGS. 56A and 56B provide representations of leaky optical fiberelements that can be used for curing in the present invention FIGS. 57Aand 57B provide representations of an embodiment of the presentinvention using leaky optical fiber elements.

FIG. 58 provides a schematic representation of a digital printing press.

FIGS. 59A and 59B provide representations of an embodiment of thepresent invention for forming −45+45 composite ply assemblies.

FIGS. 60A and 60B provide representations of an embodiment of thepresent invention for forming 0+90 composite ply assemblies.

FIG. 61 depicts one suitable chemistry for tethering inorganicdownconverter particles to the photoinitiator whereby a silica coatedphosphor is reacted with aminopropyltriethoxysilane (APTES), then themodified photoinitiator is bound to the pendant aminopropyl group.

FIG. 62 provides a block flow diagram of one embodiment of a typicalmethod of use in the present invention.

FIGS. 63A-G provide representations of stages in the production of anembodiment of the present invention for forming various semiconductor ICdevices with electrically conductive contacts and metallic heat sinks.

FIG. 64 provides a representation of an embodiment of the presentinvention wherein a lid seal is formed using a heat sink for a packagedIC that is hermetically sealed inside a cavity.

FIG. 65 provides a representation of a similar embodiment of the presentinvention wherein a lid seal is formed using a heat sink for a packagedTC that is hermetically sealed inside a cavity, and wherein a portion ofthe heat sink is replaced by a window that transmits desired wavelengthsof light received by or transmitted by the IC or combination of ICs.

FIG. 66 provides a representation of a further embodiment of the presentinvention wherein a lid seal is formed using a heat sink for a packagedIC that is hermetically sealed inside a cavity, and wherein a portion ofboth the heat sink and the heat sink support are replaced by windowsthat transmit desired wavelengths of light received by or transmitted bythe IC or combination of ICs.

FIG. 67 provides a representation of an encapsulated IC of the presentinvention, wherein the IC device is encapsulated by a glob-top formed ofa cured resin having high transmissivity.

DETAILED DESCRIPTION OF THE INVENTION

A new class of curable adhesives is provided by the present invention.This new class of adhesives has one or more of the following desirableattributes:

-   -   a—Cure without line of sight (bond line where the adhesion takes        place is internal to structures to be bonded)    -   b—Cure without depth of penetration limitation (Bond line can be        deep inside materials without compromising the cure kinetics)    -   c—Cure without thermal expansion mismatch (ability to bond at        room temp and to avoid compressive and tensile stresses at the        bond line)    -   d—Cure adhesive selectively (only where the adhesive has an        energy converting particle does the adhesive form a network;        this can be used to generate selective curing geometries)    -   e—The adhesives have suitable Properties (electrical—including        dielectric non-conductive to anisotropically semiconductive to        conductive, mechanical—rigidity or compliancy (use of a second        phase flexibilizer), optical—from transparent to opaque, Acid        vs. Base Control—ability to withstand a variety of environments        from Inks to aqueous solutions, Adhesive Bond strength of a        desirable range)

These attributes make it possible to achieve certain adhesive curingapplications which were not previously attainable, as well as improve onalready existing adhesive curing applications. The present inventionadhesive curing leads to novel assemblies and processing methods thatare advantageous compared to the state of the art.

In one embodiment, the present invention provides a way to bondmaterials at ambient temperature using photoinitiator chemistries thatconvert absorbed light energy (typically UV light) to chemical energy inthe form of initiating species such as free radicals or cations andthereby initiate a polymerization reaction in a monomer-containingadhesive. In another aspect, the invention provides a way to performphoto-initiation in situations where the area to be bonded is notaccessible to an external light source.

According to one embodiment of the invention, the adhesive compositioncomprises: an organic vehicle comprising at least one polymerizablemonomer; at least one photo-initiator responsive to a selectedwavelength of light; and, at least one energy converting materialselected to emit the selected wavelength of light when exposed to aselected imparted radiation.

According to another aspect of the invention, the method of adhesivebonding comprises the steps of: a) placing a polymerizable adhesivecomposition, including at least one photoinitiator and at least oneenergy converting material, in contact with two or more components to bebonded to form an assembly; and, b) irradiating the assembly withradiation at a first wavelength, capable of conversion by the at leastone energy converting material, preferably a down converting materialsuch as a phosphor, to a second wavelength capable of activating the atleast one photoinitiator.

According to yet another aspect of the invention, the method of adhesivebonding comprises the steps of: a) attaching the at least onephotoinitiator and at least one energy converting material with oneanother using such methods as adsorption or chemical bonding through atether and then mixing the chemistry hence formed into the mix with aresin.

According to a further embodiment of the invention, a method forcreating joints and establishing adhesion between 2 different substratescomprises using an adhesive system that in turn contains a plurality ofsynthetic polymeric chains and at least one photoinitiator that is aphotoactive cross-linking agent. In this case the role of the at leastone photoinitiator as a photo-active cross-linking agent is to link onepolymer chain to another by forming bonds that can be covalent or ionicin nature. In this case the initial viscous material is transformed to asolid material through the formation of a 3D network structure achievedby creating links between pre-existing chains in a resin system. Suchcross-linking can be applicable to both synthetic polymers (foradhesives) and to natural polymers (such as protein or DNA).

The inventive material of one embodiment of the present inventioncomprises two primary components: first, a monomer composition includingat least one photoinitiator; and second, at least one energy convertingmaterial capable of absorbing an imparted energy and converting theenergy to produce photons in a spectral range that can be absorbed bythe at least one photoinitiator, and thus initiate polymerization of themonomer composition. Preferably, the energy converting material is adownconverting material capable of absorbing higher-energy photons(typically X-rays) and down-converting to produce lower-energy photons(typically UV, but also visible light) in a spectral range that can beabsorbed effectively by the photoinitiator. Optional components include,without limitation: organic and inorganic fillers such as oxides,dielectrics, conductors, fibers, etc.; plasticizers; pore-formers; andother physical additives.

In an alternative embodiment, the curable adhesive composition comprisesa plurality of cross-linkable polymer chains rather than thepolymerizable monomer. In this embodiment, the photoinitiator is onethat is capable, upon activation, of creating crosslinks between thecross-linkable polymer chains to form a 3D polymer network, thus curingthe adhesive composition by crosslinking. While many of the embodimentsbelow are described based upon the embodiment using a curable adhesivecomposition comprising polymerizable monomer, this description is merelyfor convenience and use of the curable adhesive composition comprisingthe plurality of cross-linkable polymer chains can be equallysubstituted in the described embodiments.

In the present invention, the energy converting material can be anymaterial that can convert the imparted energy either into higher energyphotons (“upconverting material”) or into lower energy photons(“downconverting material”). Suitable upconverting materials anddownconverting materials are described in U.S. provisional patentapplication 61/161,328, filed Mar. 18, 2009; U.S. provisional patentapplication 61/259,940, filed Nov. 10, 2009; U.S. ProvisionalApplication Ser. No. 60/954,263, filed Aug. 6, 2007, and 61/030,437,filed Feb. 21, 2008; U.S. application Ser. No. 12/059,484, filed Mar.31, 2008; U.S. application Ser. No. 11/935,655, filed Nov. 6, 2007; U.S.Provisional Application Ser. No. 61/042,561, filed Apr. 4, 2008;61/035,559, filed Mar. 11, 2008; and 61/080,140, filed Jul. 11, 2008;U.S. patent application Ser. No. 12/401,478 filed Mar. 10, 2009; U.S.patent application Ser. No. 11/935,655, filed Nov. 6, 2007; U.S. patentapplication Ser. No. 12/059,484, filed Mar. 31, 2008; U.S. patentapplication Ser. No. 12/389,946, filed Feb. 20, 2009; and U.S. patentapplication Ser. No. 12/417,779, filed Apr. 3, 2009, the entiredisclosures of each of which are hereby incorporated by reference. Theimparted energy can be any desired energy as needed to penetrate thematerial between the imparted energy source and the adhesive compositionitself. For example, the imparted energy can be near-infrared (NIR),with an upconverting material to convert the imparted energy into UVphotons that can be absorbed by the photoinitiator used. Preferably, theimparted energy is X-ray energy, with the energy converting materialbeing a downconverting material, such as a phosphor or scintillator. Forconvenience, the following discussion will refer to downconvertingmaterials and the use of X-rays as the imparted energy. However, this isnot intended to be limiting of the present invention and any desiredcombination of imparted energy and energy converting material can beused, so long as the photons generated by the energy converting materialare capable of being absorbed by the photoinitiator.

The associated method comprises two essential steps: a) placing apolymerizable adhesive composition, including a photoinitiator anddown-converting material, in contact with two or more components to bebonded to form an assembly; and, b) irradiating the assembly withradiation at a first wavelength, capable of down-conversion by thephosphor to a second wavelength capable of activating thephotoinitiator. Optional steps include, without limitation: dispensingthe adhesive in a selected pattern through a needle or screen printingthe adhesive through a mask having a selected pattern; photo-patterningthe adhesive; pre-forming the adhesive into a sheet having isotropic oranisotropic conductivity; and applying pressure to the adhesive bondduring the curing process.

The dispensing of the adhesive and the adhesive properties canpreferably be adjusted to meet the following:

-   -   The dispensing can be performed using any conventional        dispensing system, including, but not limited to, dispensing        using piston or auger pumps, spin coating, spray coating, or        screen printing.    -   The adhesive can contain a tracer element for inspection, if        desired.    -   The adhesive can contain a pigment for optical inspection, if        desired.    -   The adhesive can be made to change color after curing, if        desired.

For reference purposes, listed below are generally accepted approximatewavelength, frequency, and energy limits of the various regions of theelectromagnetic spectrum:

Wavelengh (m) Frequency (Hz) Energy (J) Radio >1 × 10⁻¹ <3 × 10⁹ <2 ×10⁻²⁴ Microwave 1 × 10⁻³-     3 × 10⁹-     2 × 10⁻²⁴- 1 × 10⁻¹    3 ×10¹¹    2 × 10⁻²² Infrared 7 × 10⁻⁷-     3 × 10¹¹-     2 × 10⁻²²- 1 ×10⁻³    4 × 10¹⁴    3 × 10⁻¹⁹ Optical 4 × 10⁻⁷-     4 × 10¹⁴-     3 ×10⁻¹⁹- 7 × 10⁻⁷ 7.5 × 10¹⁴    5 × 10⁻¹⁹ UV 1 × 10⁻⁸-  7.5 × 10¹⁴-     5× 10⁻¹⁹- 4 × 10⁻⁷    3 × 10¹⁶    2 × 10⁻¹⁷ X-ray 1 × 10⁻¹¹-     3 ×10¹⁶-     2 × 10⁻¹⁷- 1 × 10⁻⁸    3 × 10¹⁹    2 × 10⁻¹⁴ Gamma-ray <1 ×10⁻¹¹ >3 × 10¹⁹ >2 × 10⁻¹⁴

Several application domains can benefit from this new class of adhesiveand methods used to cure such new class of adhesives and these include:

Bonding Of Semiconductors such as wafer bonding, die to wafer bonding,die on die bonding, package on package assembly at room temperature,etc. This is a particularly useful area for anisotropically conductiveadhesives.

Encapsulation Of Semiconductors: Such as glob top, dam and fill, molding(PMC), insertion molding and flip chip underfill.

Semiconductor lithography: the present invention adhesive compositionsand corresponding constituent material chemistries can be used in frontend semiconductors to pattern gate structures. The photolithographyapplications include the use of photoresist materials that have negativeor positive tones and development. The exposure of X-rays can be gatedby adjustable apertures (particularly those made from lead), withprogrammable distances to allow X-rays to interact with specific areasof the dispensed adhesive. Furthermore, patterning using X-rays can beperformed by masks containing heavy metals that attenuate X-ray in someareas and not others.

Other methods of patterning can bypass all mask work by using imprintlithography. In this case, dip transfer methods and stamping methods canbe used to deposit a pattern that contains the adhesive composition withfeatures containing energy converting particles. In this case X-raywould cure the adhesive areas with the conversion particles containedwithin.

The Present Invention Also Provides the Ability to Prepare NovelComposites.

A novel ply (the fundamental Building Block for composites) containsfibers coated with polymer resins, energy converting particles andsuitable catalyst/photoinitiator systems. This novel prepreg material isused for the build up process (Cross-ply, unidirectional ply) used incomposites to yield light weight structures and shapes ranging fromsimple shapes to complex 3D shapes and structures (such as a roundvessel). The stack up or build up is then exposed to X-ray for curingand solidification.

Bonding of Composites:

Bonding of composites to other composites, to metals and metal alloys,to rubbers, to leather and to inorganic materials (such as ceramics),particularly useful in bonding of non-like materials to one another.

Attaching Mechanical Fasteners to Composites:

Bonding of small metallic components to large composite panels such asrivets can be useful to fasten 2 separate structures. Conventionally,this requires the use of metal on metal contact to accomplish a weldedconnection. The present invention adhesives enable much widermanufacturing freedom of operation. For aerospace and automotiveapplications, for example, a KUKA robot (sold by KUKA Aktiengesellschaftof Augsburg, Germany) can be equipped with an adhesive applicator (suchas a dispenser) and an X-ray source as well as a pick and place machineto: dispense the adhesive, perform optical inspection, place a rivet andhold it in place, and cure with X-ray, all within a record time comparedto any other known methods. Furthermore, the advantage of roomtemperature bonding minimizes warpage.

Natural Composites:

The fabrication of large wood beams, or other natural compositematerials, is conventionally accomplished, for example, from small woodpieces by resin coating the wood pieces and bonding the assembly underhigh pressure and heat to cure the adhesive. The present inventionadhesives allow room temperature bonding and no moisture needs to bevolatized during cure. This is far better than the conventional methodsof making such composites which typically use microwaves for heatgeneration, but creates enormous amounts of heat in the process,sometimes even resulting in the workpiece catching fire!

Bonding of Metals:

bonding metallic chassis and doors in automotives (to replaceconventional induction heating). Metal sheets are bent in special shapesand then adhesively bonded together by first dispensing a bead aroundthe chassis and mating the metallic pieces, fixing their position,followed by curing using the present invention method and composition.

Fluidic Channels:

Creation of fluidic channels in plastics, metals and inorganicsubstrates by bonding patterned substrates together to form said fluidicchannels. The joining of dissimilar plastics, the joining ofsemiconductors to plastic can be done without the mismatch induced bythermal expansion.

Multichip Modules:

Die on KOVAR substrate, as well as lid sealing on multi-chip-modules.

MEMS:

Sealing MEMS with glass wafers at room temperature (without head shift).

Optoelectronics:

Alignment for maximizing light intensity yield (DWDM) and apply adhesiveand cure at room temperature (maintain maximum light intensity passage).Align fiber in V-groove and cure and align multi-channels fibers andcure while maintaining light intensity passage.

Attaching Deformable Substrates, Particularly Dissimilar Substrates:

Attaching rubber to foam, leather to rubber, leather to leather, orfabric to fabric, or any combination of deformable substrates.

Other preferred applications of the present invention adhesivestechnology include, but are not limited to:

-   -   Adhesive bonding of living tissue, not only at the surface but        internally. This eliminates the need for sutures or staples.        Currently, cyanoacrylate (“SuperGlue”) type adhesives are used        for these applications. However, cyanoacrylates generally        generate heat as they cure, which can lead to cell ablation.    -   Activation of a coagulant to treat bleeding—most valuable in a        trauma or extensive surgery. The present invention adhesives        could be used as temporary “stop-gap” measures in trauma        patients, giving the caregiver more time to address injuries        without the patient bleeding out.    -   Remote curing of construction materials, best suited for local        repair with a uniform cure throughout the articles to be cured.    -   Bonding of fabrics such as foul weather gear, without heat,        eliminating melting created at a heat bond, and the need for        putting (stitch) holes into impervious materials.

One particularly preferred application domain is in the field ofmicroelectronics assembly, where thermoset adhesives are used to bondbare die to substrate, establish conductive contacts, and performvarious roles in packaging and sealing structures such as glob-top anddie-underfill structures. Commercially available materials areformulated to meet various requirements, and in addition to themonomer(s) may contain particulate fillers such as metal or dielectricpowders, as well as various additives to control viscosity and otherproperties. The materials are typically dispensed as a thixotropic fluidin precise locations, and after all the parts are placed, the entireassembly is heated to a temperature necessary to polymerize themonomers. The present invention avoids the need to use such heating andcan generate curing of the adhesive without risking warpage or otherheat damage to the microelectronics.

As modern electronic components evolve to smaller sizes, and integratedcircuits include ever-smaller features such as ultra-shallow junctions,the permissible thermal budget during assembly continues to decrease.Similarly, polymer composites used for dental restorations must be curedwithout subjecting the patient to high curing temperatures. To addressthese issues, many photo-curing polymer systems have been developed. Ingeneral, these systems employ a photoinitiator, which, when exposed toUV light, releases chemical energy in the form of free radicals orcations to initiate the reaction of the monomers at substantiallyambient temperatures.

The clear conventional limitation of photoinitiators is the need to havedirect access to a suitable light source. This prevents the use ofconventional materials for advanced processes such as multilayer stacksof individual silicon dies, because there is no way to get the UV lightinto the interior of the stack. These limitations are not present withthe present invention adhesives, since the present invention adhesivescan be readily cured by application of ionizing radiation, such asX-rays to cure the adhesive in place with minimal heat generated.

In the description that follows, various aspects of the invention willbe described in greater detail so that the skilled artisan may gain afuller understanding of how the invention may be made and used. Althoughthe present description discusses the use of X-ray as the triggeringradiation for the curing process, other types of ionizing radiation canbe used as the triggering radiation, using similar down-convertingagents, including, but not limited to, gamma rays or particle beams,such as proton beams or electron beams.

CTE—Mismatch

The mismatch between the coefficients of thermal expansion of differentmaterials can be illustrated through the following table. The presentinvention enables joining materials without heat and hence circumventsthe stresses that are typically trapped during thermal heatingnecessitated by thermal curing adhesives. The current invention enablescuring between materials of drastically different CTEs.

Material Coefficient OF Thermal Expansion/ppm/C Silica Glass 0.6 E-Glass4.8 Alumina 8.7 Steel 14 Aluminum 23-24 Polyimide 38-54 Epoxy 45-65Polyester  55-100 Polystyrene 60-80 Polypropylene  85-200 Silicone resin160-180

Photoinitiators

The first essential component of the inventive material is a monomersystem including a photoinitiator. The radical polymerization offormulations based on acrylate or styrene has been widely developed. Ittypically relies on radiation curing using near UV (300-400 nm range),although photoinitiators are now available in the visible up to the IRrange as well as into the deep UV range. Cationic photoinitiators, whichproduce either a Lewis or Bronsted acid, may be used as initiators forcationically polymerizing materials (e.g., epoxies) and for resins thatare capable of crosslinking via polycondensation reactions.

Photoinitiators are typically divided into two classes: Type Iphotoinitiators which undergo a unimolecular bond cleavage whenirradiated, yielding free radicals, and Type II photoinitiators whichundergo a bimolecular reaction, in which the excited state of thephotoinitiator interacts with a second molecule (called a coinitiator)to generate free radicals. UV photoinitiators may be of either Type I orType II, whereas visible light photoinitiators are almost exclusivelyType II.

Type I UV photoinitiators include, but are not limited to, the followingclasses of compounds: benzoin ethers, benzil ketals,α-dialkoxyacetophenones, α-aminoalkylphenones, and acylphosphine oxides.Type II UV photoinitiators include, but are not limited to,benzophenones/amines and thioxanthones/amines. Visible photoinitiatorsinclude, but are not limited to, titanocenes.

It will be appreciated that the most efficient system will be one inwhich the particular photoinitiator is selected based on twoconsiderations, viz., the type of monomer system and the type of lightavailable.

A large number of useful photoinitiator compounds are known in the art.The following compounds [available from Sigma-Aldrich Corp., St. Louis,Mo.] have been characterized and their UV absorbance spectra areavailable: Acetophenone, 99%; Anisoin, 95%; Anthraquinone, 97%;Anthraquinone-2-sulfonic acid, sodium saltmonohydrate, 97%; (Benzene)tricarbonylchromium, 98%; Benzil, 98%; Benzoin, sublimed, 99.5+%;Benzoin ethyl ether, 99%; Benzoin isobutyl ether, tech., 90%; Benzoinmethyl ether, 96%; Benzophenone, 99%; Benzophenone/1-Hydroxycyclohexylphenyl ketone, 50/50 blend; 3,3′,4,4′-Benzophenonetetracarboxylicdianhydride, sublimed, 98%; 4-Benzoylbiphenyl, 99%;2-Benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 97%;4,4′-Bis(diethylamino)benzophenone, 99+%;4,4′-Bis(dimethylamino)benzophenone, 98%; Camphorquinone, 98%;2-Chlorothioxanthen-9-one, 98%; (Cumene)cyclopentadienyliron(II)hexafluorophosphate, 98%; Dibenzosuberenone, 97%;2,2-Diethoxyacetophenone, 95%; 4,4′-Dihydroxybenzophenone, 99%;2,2-Dimethoxy-2-phenylacetophenone, 99%; 4-(Dimethylamino)benzophenone,98%; 4,4′-Dimethylbenzil, 97%; 2,5-Dimethylbenzophenone, tech., 95%;3,4-Dimethylbenzophenone, 99%; Diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide/2-Hydroxy-2-methylpropiophenone, 50/50 blend;4′-Ethoxyacetophenone, 98%; 2-Ethylanthraquinone, 97+%; Ferrocene, 98%;3′-Hydroxyacetophenone, 99+%; 4′-Hydroxyacetophenone, 99%;3-Hydroxybenzophenone, 99%; 4-Hydroxybenzophenone, 98%;1-Hydroxycyclohexyl phenyl ketone, 99%; 2-Hydroxy-2-methylpropiophenone,97%; 2-Methylbenzophenone, 98%; 3-Methylbenzophenone, 99%;Methybenzoylformate, 98%;2-Methyl-4′-(methylthio)-2-morpholinopropiophenone, 98%;Phenanthrenequinone, 99+%; 4′-Phenoxyacetophenone, 98%;Thioxanthen-9-one, 98%; Triarylsulfonium hexafluoroantimonate salts,mixed, 50% in propylene carbonate; and Triarylsulfoniumhexafluorophosphate salts, mixed, 50% in propylene carbonate.

Other suitable photoinitiators include the various IRGACURE productscommercially available from BASF Corporation. The Key Products SelectionGuide 2003 for Photoinitiators for UV Curing is hereby incorporated byreference in its entirety. A representative chemical class ofphotoinitiators is provided as examples. It would be appreciated thatderivatives of such chemistries is also included. The representativelist includes alpha-Hydroxyketone and derivatives based on(1-Hydroxy-cyclohexyl-phenyl-ketone;2-Hydroxy-2-methyl-1-phenyl-1-propanone;2-Hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone).Phenylglyoxylate and derivatives based on (Methylbenzoylformate;oxy-phenyl-acetic acid 2-[2 oxo-2 oxy-phenyl-acetic acid 2-[2 oxo-2phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic2-[2-hydroxy-ethoxy]-ethyl ester). Benzyldimethyl-ketal and derivativesbased on (Alpha, alpha-dimethoxy-alpha-phenylacetophenone).Alpha-Aminoketone and derivatives based on(2-Benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone;2-Methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone/IRGACURE369 (30 wt %)+IRGACURE 651 (70 wt %). Mono Acyl Phosphine (MAPO) andderivatives based on (Diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide.MAPO alpah-Hydroxyketone and derivatives based on DAROCUR TPO (50 wt%)+DAROCUR 1173 (50 wt %). Bis Acyl Phosphine (BAPO) and derivativesbased on Phosphine oxide, phenyl bis (2,4,6-trimethyl benzoyl). BAPODispersion based on (IRGACURE 819 (45% active) dispersed in water).BAPO/alpha-Hydroxyketone (IRGACURE 819 (20 wt %)+DAROCUR 1173 (80 wt %).Metallocene (Bis (eta 5-2,4-cyclopentadien-1-yl), Bis[2,6-difluoro-3-(1H-pyrrol-1-yl), phenyl]titanium). Iodonium salt andderivatives based on Iodonium, (4-methylphenyl) [4-(2-methylpropyl)phenyl]-, hexafluorophosphate(1-).

The organic vehicle of the present invention can comprise apolymerizable composition or a crosslinkable composition. The termorganic vehicle is used herein to indicate the portion of the curableadhesive composition that ultimately forms the resin upon curing,whether by polymerization or crosslinking. Thus, a polymerizable organicvehicle comprises at least one polymerizable monomer. A crosslinkableorganic vehicle thus comprises a plurality of crosslinkable polymerchains. Ideally, the organic vehicle is of a suitable viscosity fordispensing/applying to the desired substrate.

The monomer system may be selected based upon overall requirements suchas strength, flexibility or compliance, matching with substrateproperties, and the type of bonding involved, such as electricallyconductive bonding versus a strictly structural adhesive bond.

Some suitable monomer systems that may be used for various applicationsof the invention include, without limitation: epoxies, phenolics,urethanes, acrylics, cyanoacrylates, silicones, polysulfides,polyimides, polyphenylquinoxalines, and styrenes. A source for suitablemonomer chemistries is “Engineered Materials Handbook: Adhesives andSealants, Volume III (v. 3)” CRC Press, 1990, by Cyril A. Dostal, thecontents of which are hereby incorporated by reference. In oneparticularly interesting embodiment of the present invention, theadhesive can be used to bond living tissue to living tissue, such as inadhesive suturing of wounds or surgical openings. Any monomer systemresulting in a polymer that is biocompatible can be used in suchapplications, with preference given to the cyanoacrylates commonlyalready used in wound care, but with an X-ray initiated cure by downconverting the X-ray into an energy sufficient to promote the curing ofmonomer based adhesive. The X-ray based curing described herein furtherincludes adhesives based on crosslinking polymeric chains throughactivation of appropriate cross-linking agents.

Energy Converting Materials

The second essential component of the inventive material is a materialcapable of converting the imparted energy and converting it to photonsin a spectral range that can be absorbed effectively by thephotoinitiator. Preferably, the energy converting material is adownconverting material capable of absorbing higher-energy photons(typically from ionizing radiation such as X-rays) and down-convertingto produce lower-energy photons (typically UV) in a spectral range thatcan be absorbed effectively by the photoinitiator. These materials arebroadly classified in two classes: scintillators and phosphors. Manydown-converter materials are known, including, without limitation: metaloxides; metal sulfides; doped metal oxides; or mixed metalchalcogenides. Also included in this category are organic-inorganichybrid scintillators such as disclosed by Kishimoto et al. (Appl. PysLett. 2008, 93, 261901), the contents of which are incorporated hereinby reference.

Many other downconverting particles, upconverting particles, plasmonicsactive particles and combinations of these are disclosed in U.S.provisional patent application 61/161,328, filed Mar. 18, 2009; U.S.provisional patent application 61/259,940, filed Nov. 10, 2009; U.S.Provisional Application Ser. No. 60/954,263, filed Aug. 6, 2007, and61/030,437, filed Feb. 21, 2008; U.S. application Ser. No. 12/059,484,filed Mar. 31, 2008; U.S. application Ser. No. 11/935,655, filed Nov. 6,2007; U.S. Provisional Application Ser. No. 61/042,561, filed Apr. 4,2008; 61/035,559, filed Mar. 11, 2008; and 61/080,140, filed Jul. 11,2008; U.S. patent application Ser. No. 12/401,478 filed Mar. 10, 2009;U.S. patent application Ser. No. 11/935,655, filed Nov. 6, 2007; U.S.patent application Ser. No. 12/059,484, filed Mar. 31, 2008; U.S. patentapplication Ser. No. 12/389,946, filed Feb. 20, 2009; and U.S. patentapplication Ser. No. 12/417,779, filed Apr. 3, 2009, the entiredisclosures of each of which are hereby incorporated by reference.

Phosphor selection criteria were based on peak intensity of theemission, peak position with UV of the emission, the need to have aworkable phosphor with minimal storage requirements, handling andpackaging, the ability of the phosphor to couple to X-ray energy, thecontrol over its particle size and particle size distribution; and,finally their surface chemistry.

The peak emission target is between 310 nm and 400 nm or simply the UVAspectrum. It is desirable to have the maximum conversion of X-rayintensity into UVA intensity. This conversion described in variousinterrelated terms. Sometimes it is referred to as the quantum yield orprobability of interaction between X-ray and phosphors. Theseinterrelated terms include the coupling efficiency, emissioneffectiveness or the Effective-Z between the X-ray and the phosphor. Alist of some of the best X-ray phosphors is reported in Table 1.

TABLE 1 Emission Spectrum X-ray Absorption Microstructure Peak EmissionEmiss Eff K-edge Specific Crystal # Phosphor (nm) (%) Eff (Z) (keV)Gravity Structure Hygroscopic 1 BaFCI:Eu²⁺ 380 13 49.3 37.38 4.7Tetragonal N 2 BaSO₄-:Eu²⁺ 390 6 45.5 37.38 4.5 Rhombic N 3 LaOBr:Tm³⁺360, 460 14 49.3 38.92 6.3 Tetragonal N 4 YTaO₄ 337 59.8 67.42 7.5Monolithic N 5 YTaO₄:Nb (*) 410 11 59.8 67.42 7.5 Monolithic N 6 CaWO₄420 5 61.8 69.48 6.1 Tetragonal N 7 LaOBr:Tb³⁺ 420 20 49.3 38.92 6.3Tetragonal N 8 Y₂O₂S:Tb³⁺ 420 18 34.9 17.04 4.9 Hexgonal N 9 ZnS:Ag 45017 26.7 9.66 3.9 Hexgonal N 10 (Zn,Cd)S:Ag 530 19 38.4 9.66/26.7 4.8Hexgonal N 11 Gd₂O₂S:Tb³⁺ 545 13 59.5 50.22 7.3 Hexgonal N 12La₂O₂S:Tb³⁺ 545 12.5 52.6 38.92 6.5 Hexgonal N

UVA/UVB Emissions

In some applications the desirable incident or initiation energy isdifferent than X-ray (such as EUV) while the desirable down-convertedoutput intensity remains in the UVA. In other applications the desirableincident or initiation energy is X-ray but the desirable down-convertedenergy output of the phosphor is in the UVB. Yet in other cases thedesirable incident or initiation energy is X-ray but the desirabledown-converted energy output of the phosphor is in the UVA and the UVB.The selected phosphors were selected to work with excitation sourcesincluding X-ray, extreme UV and e-beam. Within the X-ray regime, theselected phosphors can couple to a flux of X-ray photons emanating fromcommercially available equipment sources used for therapeutic tumortreatments, medical imaging and semiconductor inspection.

An example of a material (YTaO4) that emits in the UVA regime isprovided in FIG. 1. YTaO₄ was reported to have a peak emission at 337 nmunder X-ray and was measured during the course of the present inventionto emit at 327 nm. The X-ray system used to carry out the experiment wasthe Faxitron X-ray System. An example of a material (LaF₃:Ce) having anoutput in the UVB is provided in FIG. 2. LaF₃:Ce was reported to emit at280 nm under X-ray and was measured during the course of the presentinvention to emit at 300 nm. An example of a material (LaOBr:Tm₃+)having an output in the UVA, UVB and the visible is provided in FIG. 3.LaOBr:Tm₃+ coated with Silica was measured during the course of thepresent invention to emit in the UVB, UVA and the Visible.

Mixed or Alloyed Phosphors

Another possibility of interest is the ability to mix at least 2phosphors to broaden the output of the mixture compared with thestarting phosphors. In this example 2 phosphors each emitting in adistinct region were mixed together and the output spectral output wasmeasured to demonstrate the ability to influence the output intensity ofthe mixture compared to the starting materials. (See FIGS. 4 and 5)

The intensity of the initiation energy (X-ray in this case) influencesthe UV output of the phosphor. The following examples are provided toillustrate how modifying the intensity of photonic energy of X-ray canmodulate the light output of the X-ray. The relative intensity output ofa phosphor (CaOW₄) was measured as a function of the energy of the X-rayphotons. The X-ray energy was modified by modifying the peak voltagesthat exist between the filament and the target. The target in this casewas tungsten. The measurements were carried out using the same mass ofphosphor under 50 kvp, 90 kvp and 130 kvp. The relative intensity of theemission in arbitrary units is indicative but not conclusive in terms ofcomparing different materials. However, within the same conditions usedto conduct measurements, it is clear that the higher X-ray intensity thehigher the relative intensity of the emitted wavelength. (See FIG. 6)

The phosphors can be synthesized from different chemicals and usingdifferent processes to control their morphology, influence theirproperties and light intensity output but more importantly theirstability in ambient air environments. It is preferred to have phosphorsthat are not hygroscopic. Phosphors are easier to handle and to workwith when they are stable in water and do not contain dopants that aretoxic; however, even when phosphors are not stable in water and docontain dopants that are toxic, the particles of the phosphors can becoated using chemistry synthesis methods that leads to the build-up of aprotective coating which shields the phosphor from the environment(water for example) and shields the environment from the toxic dopant inthe phosphor (bromide for example). The protective coating can be silicaor can be diamond or diamond-like carbon. Silica can be formed usingsol-gel derived techniques. Diamond and diamond-like carbon can bederived from chemical vapor deposition (CVD) based on hydrogen-methanegas mixtures. Handling and packaging of phosphors can be achievedthrough dispersion in solution or in powder form. It was found thatsilica coated phosphors make a good powder that does not agglomerate.

In addition to high intensity, emission at the correct wavelengths,another desirable attribute of phosphors is to have low specific gravity(if possible). A low specific gravity may help avoid sedimentation andsettling when the phosphors are mixed into another media such as a resinor a resin blend containing photo-initiators.

Rheology Adjustment

The particle size of the phosphor is a relevant factor. The smaller theparticle size the higher the surface area. The small particles werefound to alter the rheology of resins containing photo-catalysts moreeffectively than larger phosphor particles. The larger the particlessize the higher the intensity output. The phosphors were found toperform well in terms of conversion of X-ray into UVA and activatingphoto-catalysts inside resin systems when they contain a particle sizedistribution (not a mono-modal particle size distribution). Thephosphors having small particles (i.e. having a high surface area) weresuccessfully used to increase the viscosity of the resin without the useof active silica (or AEROSIL). In fact, a new method was developed inthat enough phosphor nano-particles are added to adjust viscosityin-lieu of active silica. The best photo-activation and viscosityadjustment was found when nano-particles were used with a phosphorhaving particles up to the 5 microns particle size. In essence bimodaldistribution of particles helps the packing factor (or loading contentof phosphors into the resin) as well as helps in terms of rheologicalcontrol and UVA light intensity generation for the formulation ofadhesives having controllable viscosity, good curing under X-ray. Atri-modal or large distribution of particle sizes are effective inbalancing rheology of the adhesive and cure response of the adhesiveunder X-ray.

Organic Materials

In addition to the inorganic compounds (or phosphors) described in thecurrent invention, organic compounds can be used to achieve the samepurpose described in the current invention. Anthracene and anthracenebased compounds can be used to achieve the objective of the invention(curing with no line of sight and thermal energy). Anthracene exhibits ablue (400-500 nm peak) fluorescence under ultraviolet light.Furthermore, it was found that antharacene exhibits fluorescence underX-Ray energy. Anthracene light output was measured to be 40% to 50% ofNal(Tl).

Various plastic scintillators, plastic scintillator fibers and relatedmaterials are made of polyvinyltoluene or styrene and fluors. These andother formulations are commercially available, such as from Saint GobainCrystals, as BC-414, BC-420, BC-422, or BCF-10.

Peak Product Emission Phosphor Reference (nm) Organic BC-414 392 OrganicBC-420 391 Organic BC-422 370Other polymers are able to emit in the visible range and these include:

Peak # of Phosphor Product Emission Photons (Fiber Forms) Reference (nm)Per MeV Organic BCF-10 432 8000 Organic BC-420 435 8000 Organic BC-422492 8000

Furthermore, the organic compounds that can convert X-ray to UV energycan be interwoven into synthetic polymer chains. These chains can beused as the base resin system for a cross-linking adhesive; henceleading to the formation of a new set of X-ray activatable resinsystems.

A listing of downconverting phosphors in ascending peak emissionwavelengths is provided in the Table 2. Interestingly, phosphors fromthis table can be selected to provide selective emissions at peakemission wavelengths from 310-550 nm, thus providing a wide array ofpotential materials for activation of a wide array of photoinitiators.

UV receptive chemistries can be made more reactive by addingphoto-sensitizers. This process is referred to as photo-sensitization.Certain photosensitive chemical compounds can be added to supplementphotonic energy to the reactant and the reactant site to promote orenhance curing.

For UV curing applications, it is of interest to have chemistries thatupon exposure to the UV radiation would form an intermediate in anexcited state that in turn emits light of the correct wavelength forfurther curing to take place. In other words, a sensitizer plays a rolein energy transfer.

Many light sensitizing chemistries are known and widely used in theindustry and these include to name but a few, acenaphthene quinone,aceanthrene quinone, or a mixture thereof with anthrone and/ornaphthaquinone, violanthrone, isoviolanthrone, fluoresceine, rubrene,9,10-diphenylanthracene, tetracene, 13,13′-dibenzantronile, levulinicacid.

TABLE 2 Emission X-Ray Spectrum Absorption Phosphor Peak Emission K-edgeSpecific Crytal Color (nm) Emiss Eff (%) Eff (z) (keV) Gravity StructureHygroscopic Zn3(PO4)2:Ti+ 310 N BaF2 310 Slightly Csl 315 NCa3(PO4)2:Ti+ 330 N YTaO4 337 59.8 67.42 7.5 Monolithic N Csl:Na 338 YBaSi2O5:Pb2+ 350 N Borosilicate 350 N LaCl3(Ce) 350 Y SrB4O7F:Eu2+ 360 NRbBr:Ti+ 360 ? (Ba, Sr, Mg,)3Si2O7:Pb2+ 370 N YAlO3:Ce3+ 370 N BC-422370 Organic ? BaFCl:Eu2+ 380 13 49.3 37.38 4.7 Tetragonal N BaSO4-:Eu2+390 6 45.5 37.38 4.5 Rhombic N BaFBr: Eu2+ 390 ? BC-420 391 Organic ?BC-414 392 Organic ? SrMgP2O7:Eu2+ 394 N BaBr2:Eu2 400 N (Sr,Ba)Al2Si2O8:Eu2+ 400 N YTaO4:Nb(*) 410 11 59.8 67.42 7.5 Monolithic NY2SiO5:Ce3+ 410 N CaWO4 420 5 61.8 69.48 6.1 Tetragonal N LaOBr:Tb3+ 42020 49.3 38.92 6.3 Tetragonal N Y2O2S:Tb3+ 420 18 34.9 17.04 4.9 HexgonalN Lu2SiO5:Ce3 420 N Lu1.8 Y0.2SiO5:Ce 420 N ZnS:Ag: 450 17 26.7  9.663.9 Hexgonal N CdWO4 475 Slightly Bi4Ge3012(BGO) 480 N (Zn,Cd)s:Ag 53019 38.4 9.66/26.7 4.8 Hexgonal N Gd2O2S:Tb3+ 545 13 59.5 50.22 7.3Hexgonal N La2O2S:Tb3+ 545 12.5 52.6 38.92 6.5 Hexgonal N Y2Al5O12 (Ce)550 N LaOBr:Tm3+ 360, 460 14 49.3 38.92 6.3 Tetragonal N CaF2(Eu)435/300 N

Spectral Matching

It will be appreciated that the most efficient system will be one inwhich the particular photo-initiator is selected based on itsabsorption, its photo-catalysis sensitivity to the intensity of theincident radiation (i.e.; the efficiency of energy transfer).

The emission wavelength in many embodiments of the present inventiondepends on the particular downconverter material chosen to carry out thecure of the photo-catalytic reaction under consideration. Accordingly,to ensure the most efficient energy transfer from the phosphor to thephotoinitiator, the phosphors are paired with the correctphotoinitiators to match the emitted frequency/wavelength from thedown-converter material to the peak absorption of the photo-initiator.This is referred to as a spectral match in the current invention. Thespectral matching mentioned above increases the chances of successfulattempts needed to overcome the activation energy barrier gatingreactions. Table 3 shows the relative peak absorption of certainphoto-initiators and the relative peak emissions of certain phosphors.The pairing of photo-initiators and phosphors was done accordingly tothe table and successfully demonstrated as illustrated in the examples.

TABLE 3 Photoinitiator Absorption Peaks Peak Absorption Phosphor PeakEmission IRGACUR 784 398, 470 398 LaOBr:Tm3+ (coated) 360, 460 DAROCUR4265 240, 272, 380 380 CWO4:Pb 425 IRGACUR 2100 275, 370 370 YTaO4:Nb(*)410 IRGACUR 2022 246, 282, 370 370 Y2SiO5:Ce 410 IRGACUR 819DW 295, 370370 BaSO4:Eu2+ (coated) 390 IRGACUR 819 295, 370 370 SrB6O10:Pb 360DAROCUR TPO 295, 368, 380, 393 368 BaSi2O5:Pb2+ 350 IRGACUR 651 250, 340340 CsI:Na (Coated) 338 IRGACUR 184 246, 280, 333 333 YTaO4 337 IRGACUR500 250, 332 332 DAROCUR 1173 245, 280, 331 331 IRGACUR 754 255, 325 325DAROCUR MBF 255, 325 325 IRGACUR 369 233, 324 324 IRGACUR 1300 251, 323323 IRGACUR 907 230, 304 304 IRGACUR 2959 276 270

Optimization of Distance

Furthermore, the distance between a phosphor particle and aphoto-initiator influences the efficiency of energy transfer. Theshorter the distance between the photo-initiators and the phosphors thebetter chances of energy transfer leading to successful reactions willtake place. Inside a mixture of a curable system there are manyparticles and a relatively elevated concentration of photo-initiators.As a result, there is more than one distance between particles andphoto-initiators. In these cases we refer to the average distancebetween phosphor particles and photo-initiators.

The photo-initiators can be adhered onto the surface of phosphorparticles using tethering of adsorption techniques among others. In thecase of tethering, a high vs. low molecular weight would be an effectiveway to change the distance between the photo-initiators and theparticles respective surfaces. In the case of deposition throughadsorption, the distance between the surface of the phosphors and thephoto-initiators can be altered by inner-layering a coating that istransparent to the radiation emitted by the phosphors. SiO₂ is anexample of such inner layer since it is transparent to UV.

Packing factor and average distance between the phosphors and thephoto-initiators can be impacted using a surface coating. The packingfactor of a phosphor having innate surface chemistry would therefore bedifferent than that for a phosphor having a relatively thick coating.

The combination of the spectral match defined above, the averagedistance between the photo-initiators and the phosphors, the intensityof radiation generated by the phosphor particles under an initiationradiation, the particle size distribution constitutes the most efficientembodiment of the present invention.

In regards to the packing factor of the phosphors, a large enough silicacoating deposited on the surfaces of particles would change theeffective packing factor of effective density of the powder (i.e.; massper unit volume of powder). Similarly, a phosphor coated with a coatinghaving an irregular shape can further influence the mass per unitvolume. As an example a powder of an average particle size of 5 micronscan be coated with a enough silica to obtain an average size of 15microns.

The phosphor itself becomes more or less responsive to the incidentX-ray beam as a result of the coating that can alter its effectivedensity of the mass of the powder per unit volume. The probability ofinteraction between the X-ray energy and the phosphors decreases withincreasing coating wall thickness. An illustration is provided in FIG. 7where the same amount of phosphor (i.e.; the X-ray coupling agent) canoccupy a larger thickness.

By virtue of changing the concentration of phosphor or by changing theeffective packing factor of the phosphor we can influence theprobability of interaction of the X-ray energy with the phosphor filledresin. The intensity of X-ray can be attenuated differently between aphosphor that has a coating and an innate phosphor surface (see FIG. 8).

The coated phosphors can be used as the filler in the resin system. Thewidely used filler in the industry is silica. In some cases alumina andboron-nitride are used. The silicate fillers are used to substitute someof the resin volume without degrading the properties of curablematerial. The filling of silica powder leads to cost savings. Filledsystems are typically more mechanically stable and more cost effectivethan the unfilled systems.

Cure Categorization:

The UV curing materials can be diverse; but, as a generalcategorization, the following materials sets are outlined by specificresin families, associated initiators, cure mechanism and appropriateapplication. This is by no means an inclusive list but just a generalcategorization to further illustration. The current invention iscompatible with each of these categories including radical cross-linkingor polymerization, cationic crosslinking, base catalyzed crosslinking.

Radical Crosslinking:

Radical cross-linking or polymerization utilizes resin systems such asacrylates, maleates, styrenes. The initiators used in these casesinclude aromatic ketones such as phenyl-glyoxylates, phenyl-glyoxylates,alpha-amino ketones, benzildimethyl ketal, bisacylphosphine oxides,monoacylphosphine oxides, benzophenones.

The photoiniators for free-radical polymerization can generate reactivechemical intermediates such as those that occur in homolytic bondcleavage, hydrogen abstraction, photo-charge transfer. The addition ofphosphors is compatible with the photo-reactive species and does notinterfere with the basis of free radical polymerization including the2-photons based processes.

By way of illustration, a two-photon photoleachable photoinitiator suchas bisacylphosphine oxides may absorb a first photon of a givenwavelength range (for example below 430 nm) to split into anotherphoto-initiator type such as monoacylphosphine oxides that in turn canbe activated using another photon of another wavelength range (below 415nm) and lead to further radical species able to promote the formation ofhigh molecular weight polymers.

The application of free radical cure encompasses a broad set ofapplications including coatings, electronic materials, and adhesives.The novel method described in the present invention extends the use ofsuch free-radical cure into no line of site applications that cannot beaccomplished otherwise and renders the use of deeply penetratinginitiating radiation the source of energy that indirectly triggers thecure.

Cationic Crosslinking

Cationic crosslinking utilizes resin systems such as epoxides, vinylethers, oxetanes. The initiators used in these cases include diaryliodonium salts, triaryl sulfonium salts and onium salts to name a few.The applications of such cationic crosslinking are found in electronicmaterials, inks and adhesives. The addition to these special saltstriggers curing by proton generation which leads to cationicpolymerization. The phosphors described in the current invention areapplicable to cationic curing materials and their applications.

As an example of a curing with a photochemical initiators, a compoundsuch as bisazide 4,4′-diazidodibenzalacetone-2,2′-disulfonic aciddisodium salt can be added to a mix. This compound initiates thecrosslinking upon irradiation at a wavelength of 360-370 nm which is areadily available wavelength. Another example include benzophenone canbe used as a photo initiator in UV-curing applications such as inks.

Base Catalyzed Crosslinking

Base catalyzed crosslinking utilizes resin systems such as epoxy,polyol/isocyanate, and Michael addition. The mechanism of curing isbased on Lewis base generators. Applications of the base catalyzedcrosslinking extend to coatings and adhesives.

Direct X-Ray Cure:

Direct curing with x-ray energy (with or without the use of phosphors)is also possible in the present invention. For example, one can add achemical compound that has the capability of being activated directlyunder x-ray energy, such as methyl ethyl ketone peroxide (MEKP), whichis an organic peroxide, to assist in initiating the polymerization.Also, benzoyl peroxide, another compound in the in the peroxide familythat has two benzoyl groups bridged by a peroxide link, can be used toassist in the initiation of the polymerization under x-ray. The effectof phosphors and these peroxide based chemicals can be additive.

Co-Curing

In some applications it is useful to have 2 adhesive beads. One adhesivebead is filled with a phosphor having a high effective packing densityand another adhesive bead having a lower packing density. In this case,under the same X-ray energy intensity, one bead would cure faster thanthe other. In some dam and fill applications, such as in RF-ID, onecould apply a dam, cure it, and then fill and cure the fill. (See FIG.9) However, one could co-cure the 2 adhesive beads using the methoddescribed in the current invention by the ability to couple moreinitiation energy into the containment bead as compared with the filler.These methods allow the curing of the containment bead and the fillermaterial at the same time (co-curing) or curing one after the other(sequential curing). The same base adhesive can be used for both cases(possibly the same chemical formulation) with the containment beadhaving a phosphor of a different conversion efficiency than that of thefiller material. This can be readily done by proper choice of thephosphor, or content of the phosphor. In a way the adhesive beads can becured effectively at the same time but one sees more UV intensity thanthe other and cure faster than the other under the same X-ray beam.

Yet in another embodiment of the present invention, an insertion moldedpiece of plastic containing the appropriate amount of phosphor is addedas part of the material to be cured. (See FIG. 10) As a molded framethis acts as the source of UV under X-ray energy. In this case theinserted molded piece gives extra UV energy to the dam (or perimeterarea) and leads to faster curing. This allows the materials to cure moreselectively at the borders. This example describes the usefulness ofinsertion molding as described in FIG. 10.

Additionally photo-sensitizing chemistries can be used to enhance thephoto-catalytic based reactions.

Sol Gel Coating Surface Modification for Special Phosphors.

Synthesizing phosphors in the micron and nanometer particle sizes can bedone using various methods. Also various phosphors may have differentsurface chemistries. Some phosphors could be potentially hygroscopic ortoxic in high doses. One way to enable the use of hygroscopic orpotentially toxic phosphors is to form a containing barrier layer aroundphosphor particles. This has the double benefit of standardizingdifferent phosphor chemistries to have the same common surface chemistrywith predictable behavior as well as shield the phosphor inside abarrier layer. A sol-gel derived silicate coating is one method by whichthis can be achieved. Silica happens to be UV transparent and iscongruent with most oxides and most phosphors that are not hygroscopic(as listed in the phosphor table).

The protective coating can be silica or can be diamond or diamond-likecarbon. Silica can be formed using sol-gel derived techniques. Diamondand diamond-like carbon can be derived from CVD based onhydrogen-methane gas mixtures. These are but representative examples ofthe methods that are possible.

Dispersion:

The uniformity of dispersion of phosphors inside a resin is quiteimportant. A uniform distribution of phosphors inside a curable systeminfluences the homogeneity of the curable material and therefore themechanical and optical properties of the curable material. The mixinguniformity and the particles size distribution have an influence on thecuring system response in terms of cure extent as a function of timeunder the initiation energy. The uniformity of the dispersion can beshort lived if the phosphors have a high specific density leading tosettling in the resin. For this reason some surface modificationtechniques can be desirable to maintain the phosphors in suspension.

Dispersants

The surface of the phosphors can be modified for 2 general purposes. Onemethod leads to tethering or adsorbing the photo-initiators onto thesurface of the phosphors. The other method is to add dispersantchemistries to the surface of phosphors to enable the phosphors toremain in suspension after the adhesive is formulated and theingredients have been mixed together. In general phosphors are preferredto be in powder form with minimal aggregation between particles. Thedispersion of phosphor powder in a resin system can be achieved usingvarious methods. These dispersion methods keep the phosphors insuspension by limiting or preventing the potential re-flocculationcaused by the particles' Brownian motion at room temperature or attemperatures above room temperatures by 20° C. to 30° C. These slightlyelevated above room temperature are useful in dispensing the adhesivesthrough a needle using a piston or an auger pump.

The surface modification of the phosphors to maintain a uniformdispersion after mixing is important. Various organic polymer agents canbe used to increase the wetting characteristics of the phosphors intothe resin chemistry. Similarly, various dispersing agents can be addedto maintain the phosphor particles in suspension inside the mix. Thedispersing agents are built from polyurethane or polyacrylate polymericstructures having high molecular weight (3000-50000). Various dispersingagent are available in the market. The dispersants can be anchored ontoinorganic surface by virtue of surface charge (the electrostaticattraction of oppositely charged surfaces) and can be anchored oradsorbed to the organic substances like the chains in the resin byvirtue of dipolar interactions, hydrogen bonding andLondon/van-der-Waals forces. Once anchored in place the high molecularweight dispersants increase the steric hindrance for particles todiffuse too close to one another hence preventing agglomeration ofphosphors.

Tethering

The downconverting particles and photo-initiators used in the presentinvention can be added as separate components to the curable adhesiveformulation, or can be tethered to one another to provide increasedlikelihood of activation of the photoinitiator upon emission from thedownconverting particles. Tethering of photoinitiators to thedownconverting particles can be done by any conventional chemistry, solong as it does not interfere with the emission characterstics of thedownconverting particles (other than potential slight movement of thepeak emission in the red or blue direction), and so long as it does notinterfere with the ability of the photoinitiator to initiatepolymerization of the curable adhesive composition. One may also usecombinations of two or more phosphors, two or more photoinitiators, orboth, to achieve more complex curing kinetics. Further, one can useorganic downconverters, such as anthracene, rather than the variousinorganic downconverters noted above. With the organic downconverters,there are additional possibilities including, but not limited to, use ofthe organic downconverter material as a separate component in thecurable adhesive composition, tethering the organic downconverter to thephotoinitiator, as described for the inorganic downconverter particlesabove, or even incorporation of the organic downconverter groups intoone or more of the monomer components of the curable adhesivecomposition.

One suitable chemistry for tethering inorganic downconverter particlesto the photoinitiator is shown in FIG. 61, whereby a silica coatedphosphor is reacted with aminopropyltriethoxysilane (APTES), then themodified photoinitiator is bound to the pendant aminopropyl group.

Other possible modifications include, but are not limited to, thefollowing:

-   -   a. Modification of existing Adhesives by adding special        downconverting particles from X-ray to UV in the range of        susceptibility of a Photoinitiator

Rheology & Cost of Phosphors

Because the surface area (and hence the overall surface energy) of thenano-sized particles is very high, the viscosity rises quickly with theaddition of a small amount of nano size powders. This limits the amountof filler that can be added. On one hand this limits the UV intensitythat can be emitted by the phosphors under X-ray energy. On the otherhand the limited filler loading that can be achieved is not economicallyfavorable since fillers are typically less expensive than the baseresins and catalysts. Furthermore, the viscosity increase with theaddition of nano-size particles becomes excessive which limits the useof the adhesive to certain application categories but not others. Inmost adhesive application it is favorable to use micron size particleswhen possible. Though as stated earlier, the best mode calls for abi-modal particle size distribution consisting of mixture of nano andmicron size particles.

In general SiO₂ is more cost effective compared to phosphors. This isnot always the case. One method by which enough UV light output isachieved while safeguarding a favorable economic phosphors-utilizationis to build a composite particle based on SiO₂ as the core particle anddecorated with the appropriate phosphors in terms of type andconcentration necessary to achieve the targeted photo-catalyticreactions (i.e.; the right wavelength output and luminosity or intensityoutput).

Building Composited Particles

In applications that require the use of micron level particles that arecost effective down converters, the surface of a carrier particle madeof silica can be decorated with desirable phosphors with nanometerparticle size. The phosphors are chosen for the right emission UVwavelength and intensity under X-ray.

The downconverting particle comprises a composite of nanoparticles and asilicate carrier particle. The silicate carrier particle has the samesurface characteristics as a particle typically used as a filler(including silica). In this case the down converting particles arebonded to the surface of the base carrier particle followed by a coatingas shown in FIGS. 11A and 11B.

By way of illustration the construction of such a composite particle ishereby provided. This description is non-inclusive of all thepossibilities but provides one viable synthesis method.

The core or carrier particle can be made of glass, such as SiO₂ oralkali-lead-silicate and have a diameter of about 2 microns.Nanometer-scale downconverting particles are applied to the surface ofthe core particle, and subsequently made to adhere or bond to thesurface of the core particle (see FIG. 11B). Some of the methodsenabling this bonding process include precipitation techniques from asolution. Another method is based on condensation by heating thedownconverting particles to much elevated temperatures compared to thecore particles while maintaining the silicate based particles abovetheir softening point. At the correct respective ranges of temperature,which are readily determined by one of ordinary skill in the art basedon the compositions of the core particle and downconverting particlechosen, the downconverting particles and the carrier particles areforced into contact, leading to condensation, thus allowing surfacedeposition to take place. The downconverting particles can be any of thephosphors listed in the table.

Quantum Dots and Alloyed Derivatives—

The downconverting particles, for example, can be quantum dots with thesuitable range of downconversion from X-ray to UV. The quantum dotsand/or oxides used for the downconversion process can further compriseelements, or alloys of compounds or elements tuned for plasmonicactivity (see FIG. 12). In a preferred embodiment, the quantum dotspreferably comprise a mixture of zinc sulfide and zinc selenide, morepreferably in a ratio within a compositional window of 60% zinc sulfide,40% zinc selenide to 70% zinc sulfide, 30% zinc selenide. The metalalloys used for plasmonics comprise silver/gold mixtures, morepreferably within the compositional window of 60% silver and 40% gold,to 70% silver and 30% gold.

After the carrier core particle is decorated with the down convertingparticles, coating the outer layer is desirable to encapsulate andprotect the down converting particles as well as modify the surface. Theouter layer coating can be accomplished using sol-gel processingfollowed by heat treatment. This leads to the formation of a compositedparticle consisting of a core particle with down-converting particles onthe surface and the whole is coated with a silicate coating. (see FIG.13). This special filler particle is used to replace an existing fillermaterial.

Tethering to Composite Particles

The present invention includes special provisions for a modified use ofexisting photoinitiators by tethering the photoinitiator tonanoparticles having downconverting properties. This close proximity ofnanoparticle to photoinitiator maximizes the chance for photoinitiationor photo-catalysis, and can achieve improved cure efficiencies. (seeFIG. 14)

In the tethered case, the downconverting particles are added duringmixing an adhesive preparation using tethered particles on a carrierparticle and mixing into the adhesive. As an alternative embodiment, thetethered photoinitiator and downconverting particles can be positionedon the surfaces of micron level carrier particles. (See FIGS. 15A and15B) The carrier particles are then used as filler. This time no surfacecoating is necessary and the photoinitiator is in direct contact withthe resin. (FIG. 15A). Alternatively, this arrangement can also use acoating of SiO₂, on which are tethered the photoinitiators. (FIG. 15B).

Since in this particular embodiment, micron size particles (largeparticles) are added to the mix, the impact on adhesive rheology isminimized compared to adding nano-size particles. This method can thuspresent added advantages, including the ability to use the micron sizeparticles as a filler to otherwise alter the cured adhesive or polymerproperties.

Brighter Composite Particles

Achieving brighter particles can be done by having the carrier particledecorated with 2 layers of phosphors. First the carrier particle isdecorated with nano-sized phosphors (FIG. 16A), then coated using solgel derived silica and lastly decorated a second time with phosphors ofthe correct size (FIG. 16B). This technique can be repeated to obtainmore phosphors or down conversion particles at the outer-layers of thecarrier particles.

Surface Preparation:

Adhesion develops through various factors including mechanicalinterlocking, adsorption, electrostatic, diffusion, weak boundary layer,acid base, chemical (covalent bonding), etc. In general, the greater thesurface irregularities and porosity at a joint area, the greater thejoint strength. The greater the compatibility of the size of theadhesives and the interstices in the adherend, the greater the bondstrength can be. Roughness of the surfaces can increase or decrease thejoint strength.

The factors affecting joint strength include: surface energetics(wetting), intrinsic stresses and stress concentrations, mechanicalresponse of various bulk phases and inter-phases involved, geometricalconsiderations, mode of applying external stresses, mode of fracture orseparation, visco-elastic behavior.

The wetting and the setting of the adhesive bead is important for a goodbond formation. The spreading co-efficient of an adhesive depends on thevarious surfaces and associated surface tensions involved. The surfacetensions are referred to here as the energetic requirements. Thesubstrate (solid), the adhesive (liquid) and the vapor (open air in mostcases) all play a role. Wetting of the surface depends on the surfaceenergy between the solid and the liquid, the liquid to vapor surfacetension and between solid to vapor surface tension. Substrates such asTeflon, PET, Nylon, PE, and PS have low energy. Substrates such asmetals, metal oxides, and ceramics have high energy.

The adhesive chemistry (the liquid in this example) can be tailored toadjust the energetic requirements at the various surfaces. But that isnot sufficient. For example, most RTV silicone resins fulfill theenergetic requirements but give negligible adhesion unless primers areused. Adhesive joints can be made stronger by surface treatments of thesurfaces to be joined. Also inter-phases can be made between theadherend and the adhesive.

For the above considerations (surface energetic requirements and primerstreatments) many surface modification techniques are used to achieve thegoal of strong and durable adhesion at joints. The treatment of polymersurfaces is used for various reasons including one or more of thefollowing list extending to making the polymers more adhesionable,increase their printability, make them more wettable, provide anenclosing layer, improve tribological behavior, potentially prepare themfor metal plating, improve their flame resistance, provide antistaticproperties, control permeation.

Dry surface modification includes, but is not limited to, a surfaceplasma ionized through RF or microwave, flame, UV, UV sensitized, ozone,UV/ozone, X-ray, LASER, electron beam, ion bombardment, and frictionagainst other materials.

Wet surface modification encompasses chemical reactions such asoxidation, sulfonation, ozonation, phosphatization, chromate conversion,amination, grafting, selective etching, deposition of coupling layers(silanes), surfactant adsorption, photochemical compounds, solvent(surface swelling), prevention of diffusion of low molecular weightmaterials to the surface, and others.

Method of Use

One embodiment of a typical method of use in the present invention canbe summarized in FIG. 62.

APPLICATIONS AND EXAMPLES List of Numbered Items in Figures

-   10: Anisotropic Conductive Polymer Sphere-   10′: Anisotropic Conductive Polymer Sphere—Partially Flattened-   11: Anisotropic Conductive, UV or Visible Light Emitting, Polymer    Sphere-   11′: Anisotropic Conductive, UV or Visible Light Emitting, Polymer    Sphere—Partially Flattened-   20: Polymer Core-   20′: Polymer Core—Partially Flattened-   22: Nickel Plating-   22′: Nickel Plating—Partially Flattened-   24: Gold Plating-   24′: Gold Plating—Partially Flattened-   26: Down-Converting Photon Emitter Coating-   26′: Fractured Down-Converting Photon Emitter Coating-   28: Flip Chip Device-   30: Substrate-   32: Flip Chip Device Bumps-   32′: Substrate Solder Bumps-   34: Matrix Epoxy Resin-   35: X-ray activated, UV or Visible Light curable, Anisotropic    Conductive Adhesive (ACA) epoxy-   36: Polymer Coating-   36′: Fractured Polymer Coating-   38: Down-Converting Photon Emitters-   39: Wafer Aligner and Bonder-   40: Top Integrated Circuit (IC) Wafer-   41: Bottom Integrated Circuit (IC) Wafer-   42: Thru Silicon Via (TSV) Contacts-   44: Vacuum Plate-   46: Split field prism and lens device-   47: Fixed lens-pair-   48: Applied Force-   49: Top wafer alignment fiducial-   49′: Bottom wafer alignment fiducial-   50: X-ray Exposure Device-   51: Superimposed alignment fiducials-   52: X-ray Imaging Detector-   60 Adhesive material-   60-1 Liquid Encapsulant (Underfill)-   60-2 Liquid Encapsulant (No Flow Underfill)-   60-3 Liquid Encapsulant (Glob Top)-   60-4 Liquid Encapsulant (Dam)-   60-5 Liquid Encapsulant (Molding)-   60-6 Thermally conductive Adhesive-   60-7 film adhesive with proper resin and the proper phosphors and    photo-initiators-   60′ adhesive bead with modified rheology for screen printing-   60″ adhesive fillet-   70 adhesive dispenser-   72 Substrate-   72′ PCB-   72″ High Density Circuit-   73 UV source-   74 Spacer element-   75 Computer Control-   76 Mechanical Drive-   77 Mechanical arm-   78 Mechanical Coupling-   79 Platen-   79′ Vacuum ports-   79″ Thermode-   80 Composite substrate-   81 PET component-   82 X-ray source-   100 Well joint features-   101 protrusion piece-   102 fluidic channels in PET-   102′ fluidic channel in LCP-   130 Pick & Place-   131 Vacuum-   132 contact pads-   132′ Wire Bond-   133 metallic lid-   133′ glass lid-   134 Flexible Circuit-   140 a plastic with injection molded features-   140 b plastic with mirror image injection molded features-   140 c bonded plastics-   150 PET plastic with well-   150′ Liquid Crystal Polymer

An example of an application and how these steps are used is provided inthe following paragraphs. One preferred embodiment involves the bondingof a silicon integrated circuit, either to a substrate or to anotherintegrated circuit (to make a multilayer stack). The penetrating powerof X-rays will be such that the X-rays can pass through the uppermostlayer of silicon and reach the bond layer, in which the downconvertingparticles will become stimulated and emit the desired wavelength oflight (which may be UV or visible, depending on the particularphotoinitiator being used).

Optional steps may include, without limitation: dispensing the adhesivein a pattern that will allow the adhesive to flow under a componentthrough capillary action (e.g., “die underfill” processes);photo-patterning the adhesive; and applying pressure to the adhesivebond before and/or during the curing process.

Other applications will involve the following steps as shown in FIG. 62:

1. (optional) surface prep—the surface must be placed in a state inwhich the adhesive to be formed can bond to the surface. This prep caninclude a variety of different methods, including but not limited to,alcohol swabbing, plasma treatment, acid or base treatment, physicalabrasion or roughening, a detailed overview of surface preparation wasprovided.

2. applying adhesive to the substrate—the adhesive can be applied usingany desired method, depending on the viscosity of the pre-cured adhesivecomposition.

3. (optional) optically inspecting the applied adhesive for dispensingquality—this is to ensure that the adhesive has been applied properly,whether evenly coated, applied in drops or lines, etc. This steppreferably requires that there be a visual contrast between the adhesiveand the substrate to which it is applied. Such a contrast can beprovided through the addition of one or more conventional coloringagents to the adhesive, or through the use of color-changing adhesivesthat change color upon curing.

4. placement of the substrate for cure—this ensures that the pieces tobe adhered together are in proper alignment.

5. Curing using X-rays and performing final inspection

6. (optional) Providing real-time closed loop feedback in an automationline (via reel to reel or islands of automation) This permits defects tobe detected much earlier in mass production, thus minimizing waste dueto misalignment of pieces or incomplete cure

Conductive Fillers

Optional components may include various organic or inorganic materialsand additives to perform desired functions, such as modifying theelectrical conductivity and dielectric properties of the cured polymer.Many of these components are well known to those skilled in the art.

Conductive fillers may include finely divided particles of metalsincluding gold, silver, nickel, copper, and alloys such as Au—Pd, Ag—Pd,etc. Other conductive phases that may be used with the invention includeLaB₆ as well as various conductive oxides and carbon. The conductivefiller particles may alternatively be made from small polymer beads orspheres having a conductive coating thereon, such as a thin gold film.The polymer particles may be fairly rigid or they may have some degreeof flexibility or compressibility in order to make the final bond morecompliant. Plasticizers and flexiblizers can be added Isotropicconductivity may be achieved by using small particles (“small” meaningparticles with an average diameter much less than the final bond or filmthickness) loaded to a volume fraction that exceeds the percolationthreshold so that the resulting polymer composite material exhibitssubstantial electrical conductivity in every direction. Conversely, theinvention may also be used for anisotropic conductive materials, inwhich a film or sheet contains a monolayer of large individual sphericalconductor particles (“large” meaning particles whose diameter iscomparable to the final bond or film thickness) loaded to a volumefraction below the percolation threshold so that the resulting materialis substantially conductive through the film thickness but is notconductive parallel to the plane of the film.

Other suitable filler materials include various dielectric materialssuch as metal titanates and zirconates, titanium oxide, etc., that maybe added to tailor the dielectric properties of the film. Otherinorganic additives may include boron nitride for applications where itis desired to have a bond that is electrically insulating yet thermallyconductive.

Organic additives may include several classes of agents familiar in theart. These include, without limitation: plasticizers to modify themechanical properties of the cured polymer; surfactants and dispersantsto modify the rheology of the uncured material to make it easier todispense as well as to allow any particulate fillers to be adequatelydispersed; and solvents and comonomers.

Conductive Polymer Spheres:

One example of an anisotropic conductive polymer sphere is generallyrepresented at 10 of FIG. 17. In this example, the sphere consists of anelastic polymer core 20 that is surrounded with a thin layer of platednickel 22 under plated gold 24 and an outer layer of another, morebrittle, thin polymer coating 36. As is well known within the art,Anisotropic Conductive Adhesives (ACA) can be manufactured from rapid(snap-cure) thermo-setting epoxy resins filled with approximately 4% ofconductive polymer spheres which have a nominal diameter of 5-microns.The polymer spheres are designed to deform elastically when compressed,exposing the outer gold plated surface, which is then able to establishelectrical continuity across the narrow gap between aligned contact padsof stacked IC chips, wafers or other substrates.

When compressed and deformed the polymer sphere 20′ becomes partiallyflattened, as generally illustrated at 10′ of FIG. 18. As the diameterexpands under compression the brittle outer polymer coating becomesfractured 36′ at the top and bottom contact surfaces and exposes themalleable and partially flattened gold plating 24′. The gold platingstill adheres to the partially flattened polymer sphere 20′ by means ofthe plated nickel layer 22′, which is also malleable and becomespartially flattened. As the plated gold metal becomes exposed undercompression it establishes a metal-to-metal electrical contact with themetal pads disposed directly above and below the partially flattenedpolymer sphere. Electrical continuity is then achieved across the gapbetween top and bottom pads around the circumference of each polymersphere thru the plated nickel and gold layers. This process is furtherdescribed and illustrated in FIG. 19.

The first essential step of the inventive method is to place apolymerizable adhesive composition, including a photoinitiator anddownconverting phosphor, in contact with two or more components to bebonded to form an assembly. As noted above, the viscosity of theadhesive may be varied over a significant range by the choice ofmonomer(s), the possible use of solvents, the loading of fillerparticles, etc., as is well understood by skilled artisans.

Many of the inventive compositions will be thixotropic, enabling them tobe conveniently dispensed using standard processes familiar in the fieldof adhesives. In particular, for microelectronics assembly, thecompositions may be applied to selected areas using automatedneedle-type applicators in conjunction with pick-and-place methods.Alternatively, they may be applied in various patterns using printingthrough screens or masks. Low-viscosity systems, which would typicallycontain solvents and a minimal amount of inorganic fillers, may bedistributed in selected patterns by ink-jet printing.

In order to form an aniostropically conductive bond, the inventivematerial may be formed into a sheet having conductive balls of theappropriate diameter, cut or diced to a desired size, and placed betweenthe two components to be bonded. It will be understood that in somecases, this process may be repeated in order to make a multilayer stackof any desired number of components.

The second essential step of the inventive method is to irradiate theassembly with radiation at a first wavelength, capable of downconversionby the downconverter to a second wavelength capable of activating thephotoinitiator, thus initiating the polymerization of the adhesive.

Applicants contemplate that in a most preferred embodiment, theradiation applied to the assembly after the bond material has beenplaced will be X-rays. Many industrial X-ray generators are availablecommercially from a number of suppliers, and the skilled artisan mayeasily select an appropriate X-ray source based upon routine engineeringconsiderations.

Conductive Resin or Adhesive Compositions

The resin or adhesive composition of the present invention can be madeconductive in a variety of ways. The use of conductive fillers has beendiscussed above and is one way to make the resin or adhesive compositionof the present invention into a conductive or semiconductivecomposition. An alternative embodiment of the resin or adhesivecomposition of the present invention uses the conductive polymer spheresas an additive to render the composition conductive. The use ofconductive polymer spheres can provide isotropic or anisotropicconductivity to the composition, depending on which type of polymersphere is used. In the event of use of an anisotropic polymer sphereadditive, the resulting composition can be rendered anisotropicallyconductive (i.e. conductive in one plane or along one axis, whilenon-conductive in a perpendicular plane or axis) by the application ofpressure alone or application of pressure and x-rays.

In a further embodiment of the present invention, the resin or adhesivecomposition can be rendered conductive without the need or use of anyadditive, by appropriate modification of the polymer forming the resinor adhesive composition. Conductive polymers or, more precisely,intrinsically conducting polymers (ICPs) are organic polymers thatconduct electricity. Such compounds may have electrical conductivity orcan be semiconductors. The conductivity of the polymer can be generatedin a variety of ways, such as by extended conjugation through thepolymer backbone, particularly through various aromatic rings along thepolymer backbone, and can include all carbon based polymers as well asheteroatom containing polymers. Suitable conductive polymers can includeany type of polymer, including but not limited to, poly(fluorene)s,polyphenylenes, polypyrenes, polyazulenes, polynaphthalenes,poly(pyrrole)s (PPY), polycarbazoles, polyindoles, polyazepines,polyanilines (PANI), poly(thiophene)s (PT),poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene sulfide)(PPS), poly(acetylene)s (PAC), poly(p-phenylene vinylene) (PPV). In thepresent invention, even if the polymer is not formed by the initiationprocess triggered by the energy emitted from the energy convertingmaterial, variants of the polymer can be used such that a low molecularweight polymer or oligomer is part of the organic vehicle, and uponapplication of the external energy (such as x-rays), the energyconverting material converts the external energy into energy to activatethe initiator, which then generates a reaction causing either chainextension or cross-linking of the low molecular weight polymer oroligomer, thus forming the final conductive resin or adhesive.

Thermo-Set Adhesive:

With the surfaces held in compression, using an externally appliedforce, the thermo-set epoxy is rapidly cured in order to maintain theconductive polymer spheres in a state of compression after the externalforce is removed. A thermo-set epoxy may be rapidly cured by means of anappropriate heat source such as a cartridge heater, microwave orultrasonic generator, IR heat lamp, laser beam, or various other meansto apply heat to the surfaces being bonded. However, the heat mustgenerally be fairly high (>250° C.) in order to achieve rapid curing ofthe epoxy and often requires that the heat be conducted through thesurfaces used for achieving the applied force as well as the chip and/orsubstrate being bonded together. If the materials being electrically andmechanically bonded exhibit a significant difference in theircharacteristic coefficient of thermal expansion (CTE), a high state ofshear stress may exist between these surfaces after the epoxy is curedand the materials return to room temperature. This shear stress isundesirable, as it may lead to a premature failure of electricalcontinuity between the aligned contact pads. This problem is morepronounced when there is a large difference in relative size between thematerials being bonded.

Several significant advantages may therefore be realized if the epoxycan be cured without the necessity for using high heat. For example, ifthe epoxy can be cured at room temperature the materials may be joinedwithout any residual shear stress thereby improving reliability. And ifthe fixtures used for aligning the parts and applying a compressiveforce between surfaces remain at room temperature, the time required forassembly may be substantially reduced.

UV or Light-Cured Adhesive:

One possible solution for rapid adhesive curing at room temperature isthe substitution of a ultraviolet (UV) curable or visible light curableadhesive for manufacturing the ACA adhesives described above. Someliterature has been written on this subject, but a fundamental problemarises when attempting to expose the adhesive to sufficient (curing) UVor light energy through optically opaque surfaces that are commonlyencountered in microelectronic assembly. Without adequate UV or visiblelight illumination the epoxy may not fully polymerize. Somemanufacturers attempt to remedy this situation by combining propertieswithin the epoxy that allow it to be partially cured with UV-energyfollowed by a final thermal cure. However, an ideal UV or light-curableepoxy for ACA applications would be realized if it can be fully curedwithout necessity of an external UV or visible light source oradditional thermal-cure steps.

As noted above, various photoinitiator compounds and downconvertingmaterials exist that can convert absorbed higher-energy (X-ray) photonsto lower-energy photons (UV or visible light). If an adhesive epoxy iscustom engineered to be sensitive (i.e. polymerize) when exposed to thespectral wavelength and energy level of one or more types of these“down-converting” lower-energy photon emitters, included as a “filler”within the epoxy, then the epoxy can be fully cured, even throughoptically opaque materials, by exposing it to an X-ray source. An addedbenefit is that the same X-ray energy may simultaneously be detected andconverted into an image for quality control purposes.

An example of an X-ray activated, UV or visible light curable,anisotropic conductive adhesive (ACA) (35) is shown in FIG. 19. Featuresof the figure are exaggerated to illustrate how an integrated chip (IC)can be assembled as a flip chip device (28) and electricallyinterconnected to a substrate (30). The bumps (32) on the bottom surfaceof the flip chip device are raised above the otherwise planar surface ofthe IC chip. The raised bumps are typically fashioned using eitherelectro-plated or electro-less plating methods and may consist of metalssuch as nickel-gold, copper-nickel-gold,titanium-tungsten/copper/nickel/gold and other various metals and/oralloy combinations. The raised bumps typically range in height from 5-10microns above the planar surface of the IC. The raised bumps aretypically formed on the chips while they are still part of the wholewafer. However, the substrate will typically not include raised bumps.When assembled in a face-down (flip chip) configuration, the raisedbumps on the IC form a difference in thickness of the gap between thesurfaces. And when properly filled with a sufficient amount and diameterof ACA polymer spheres (approximately 4% of 5 micron diameter spheres)there is a high probability that one or more spheres will be capturedbetween the flip chip device bumps and the substrate pads (not shown)and partially flattened (10′) when a proper amount of external normalforce is applied. The “proper” amount of force required is determinedexperimentally depending on the variable geometries and materials thatare being assembled. The remaining AC polymer spheres (10) that fallbetween adjacent bumps will remain un-compressed and will not generallyconduct electricity, since the brittle polymer coating (36) is unbroken.

In the example illustrated in FIG. 19, the X-ray activated adhesive (35)is also filled with small down-converting photon emitters (38) which areengineered to emit lower-energy photons in the UV or visible lightspectrum. The amount and size of these down-converting photon emitterswould also be experimentally determined, depending on the materialproperties. In practice, the down-converting photon emitter particleswould be smaller than the AC polymer spheres (10 or 10′) and would beevenly distributed within the epoxy resin (35).

Adding the down-converting photon emitters as separate “filler” mayadversely effect the viscosity and thixotropic characteristics of the UVadhesive. Therefore, an alternative and better practice would be tosubstitute the polymer coating (36) of the ACA polymer spheres (10) witha coating (26) consisting of the down-converting photon emittermaterial(s), to form a new type of anisotropic conductive, UV emitting,polymer sphere (11) as illustrated in FIG. 20. In this example thedown-converting photon emitter coating is both electricallynon-conductive and brittle in nature, so as to fracture when partiallyflattened (26′) and thereby expose the gold coating (24′) underneath, asillustrated in FIG. 21.

FIG. 22 is similar to FIG. 19, but illustrates the absence of thedown-converting photon emitter “filler” particles (38) and substitutionof anisotropic conductive, UV emitting, polymer spheres (11 and 11′), aspreviously described. These polymer spheres would be similar in size andvolume to existing ACA adhesive formulations and therefore would beexpected to perform in a similar manner.

Another example of an assembly using anisotropic conductive, UVemitting, polymer spheres (11 and 11′) is shown in FIG. 23. Thisillustration shows two similar IC wafers, such as memory chip wafers,stacked one above the other and electrically and mechanically joinedtogether. Both the top IC wafer (40) and bottom IC wafer (41) include“Through Silicon Via” (TSV) contacts (42) that provide a means forrouting circuit interconnections from the top (active) surface of thewafer to pads arrayed across the bottom surface of the wafer. In thismanner electrical functions that are present at a pad on the top(active) side of the wafer may also be present on the opposite or bottom(non-active) surface of the wafer; much like a thru-hole connectionenables signals to be routed through a printed wiring board (PWB). TheTSV contacts include small, raised, annular or square pads on the topand bottom surfaces that form contact surfaces for electrical connectionthrough the partially flattened polymer spheres (11′). When the wafersare properly aligned and compressed the X-ray activated, UV or visiblelight curable, ACA epoxy (35) is cured by exposing the assembly to anX-ray source.

X-Ray Aligner and Bonder Description:

To commercially implement the UV adhesive bonding technology describedabove, it is deemed desirable to have equipment engineered to safelyprovide the correct X-ray exposure dosage in order to activate (in situ)the UV or visible light curable adhesive, and to simultaneously imageand record the resulting cured bondline using the same X-ray energy.Some examples of suitable X-ray aligner and bonders are partiallyillustrated in FIGS. 24A-C, 25A-C and 26A-C.

An X-ray wafer aligner and bonder (39) of FIG. 24A is designed to enablewafer-to-wafer alignment and bonding using an X-ray activated, UV orvisible light curable, ACA epoxy (35) without need for applying externalheat to the wafer surfaces being joined. The bonder includes two vacuumplates (44), of sufficient size to hold a top IC wafer (40) and bottomIC-wafer (41), that are spaced apart sufficient to enable a split fieldprism and lens device (46) to be temporarily inserted and scannedbetween the surfaces, as shown. The prism device is used to preciselyalign the wafer surfaces with respect to one another, either manually orby automated means, prior to the wafer surfaces being compressedtogether. The prism device provides a means to view and superimposefiducial images from multiple locations on the bottom surface of theupper wafer with similar fiducial images on a top view of the lowerwafer. Once these fiducial images are superimposed and accuratelyaligned, the split field prism and lens device are removed and thewafers are brought together under an applied force (48) as shown in FIG.24B. The applied force compresses and partially flattens the anisotropicconductive polymer spheres (10′ or 11′) trapped between the aligned flipchip device bumps (32) and/or Thru Silicon Via (TSV) contacts (42) ofeach IC on the two wafers, as previously described and shown in FIGS.19, 22 and 23. Once the wafers are under an applied force, sufficient toenable the ACA polymer spheres to partially flatten and establishelectrical conductivity across the juxtaposed bumps or contacts, anX-ray Exposure Device (50) and X-ray imaging device (52) are broughtinto position, as shown in FIG. 24C. X-ray exposure device (50) is usedto generate a field of high energy photons that stimulate thefluorescent coating of the down-converting spheres which thenspontaneously emit UV light of the correct wavelength and luminosity tocause the UV resin to rapidly cure by photo initiation. As the highenergy photons pass through the materials they may also advantageouslybe detected on the surface of an X-ray imaging detector (52), positioneddirectly across from the X-ray exposure device and on the opposite sideof the wafer vacuum plates. The X-ray imaging detector is designed toproduce high resolution X-ray images of the bonded surfaces using analogand/or digital circuitry that is immune to damage from the X-ray source.Data from the X-ray imaging detector is collected and processed intohigh-resolution digital images, as either individual photos and/orcontinuous video, for data (archival) storage and/or image processing toprovide a means for process and quality control.

An alternative technique to achieve wafer-to-wafer alignment isillustrated in FIGS. 25A-C. In these illustrations, the movable splitfield prism and lens devices (46) are replaced by a pair of fixed lens(47) that remain stationary as the wafers are individually moved over orunder the field of view of the lens-pair to locate alignment fiducials(49 and 49′) disposed at multiple locations near the edges of both topand bottom IC-wafers. Alignment fiducials for the top IC-wafer (49)differ from the bottom IC-wafer (49′) and are designed to besuperimposed over each other to provide an optical reference for precisealignment in the x-axis, y-axis and theta-angle. When properly aligned,the fiducial images (49 and 49′) as shown in FIGS. 25A and 25B would besuperimposed, as illustrated at 51 of FIG. 25C.

Disposed on the top and/or bottom IC-wafers (40 and 41) are coatings ofa UV-curable, ACA filled epoxy (35) and/or compatible matrix epoxy resin(34). In some applications it may be desirable to apply epoxy coatingson both top and bottom IC-wafers with differing compositions andviscosities to enhance the bonding process. For instance, the bottomepoxy coating may include ACA conductive spheres (10 or 11) within ahigh-viscosity resin matrix, whereas the top IC-wafer may be coated witha compatible resin that has a lower viscosity and does not contain anyACA conductive spheres. The differing compositions and viscosities ofthe coatings allow for a reduction in the amount of ACA spheres requiredto achieve reliable interconnect between stacked chips or wafers,enables better retention of individual ACA spheres where required on thebumped pads during application of the compressive force during bonding,and helps to reduce formation of voids within the cured epoxy.

As described earlier, once the top and bottom wafers are opticallyaligned with respect to one another, the surfaces are brought togetherand compressed under an applied force to enable the ACA polymer spheresto deform and establish electrical continuity between juxtaposed pads ofthe individuals IC devices on the wafers; thereby establishing a 3-Dinterconnect between surfaces. Since the pads that are to be joined maynot have identical coefficient of thermal expansion (CTE) values, thepolymer spheres provide a compliant interface that helps to absorbexpansion mismatch during thermal cycling, thereby maintaining properelectrical continuity.

The resin and the photo-initiator materials were obtained from BASF. Thematerials were weighted in the proper ratios using a balance having+/0.1 grams measurement accuracy.

The materials were mixed in a laboratory environment with DCA (a class10,000 clean room). All materials handling was done in a fume-hood. Thelaboratory had a fluorescent light source to light the room while thefume hood had a controlled light (no UV component to it).

The substrates used to demonstrate bonding included glass,polycarbonates, poly ethylene terephthalate, poly-imides, cellulose (orpaper), cross-ply carbon-prepreg composites, PEC, ABS, Mylar, intrinsicsilicon, doped silicon, silicon based integrated circuits.

In some cases, the materials were mixed in the proper ratios then theywere transferred to syringes and subsequently centrifuged to removeair-bubbles. In other cases, the materials were placed in syringes butnot centrifuged. Yet in another case the materials were enclosed insideof the mixing cups. Depending on the specific density of the materials,a high level or a low level of sedimentation was observed.

The materials preparation further included the addition of dispersantsin an attempt to control sedimentation. In these cases the surface ofthe phosphors was modified to enable the attachment of dispersants. Thematerials were then mixed inside resin materials and photo-initiatorsunder heat. The materials were hand mixed using a stainless steelspatula that did not react or contaminate the raw materials. Nomaterials contaminations were at play for the most part. The temperatureused for mixing varied from room temperature to 80° C. The mixing wasbetter when conducted at elevated temperatures.

Raw Materials Sources

The sequence of mixing was investigated. Various mixing sequences maywork. However, a preferred embodiment of preparation is obtained byheating the resin materials to 80° C. followed by adding thephoto-initiators and mixing. The mixing and heating of the resin andphoto-initiators is continued until a clear (air bubble free) solutionis obtained. Mixing is done gently to avoid shearing the resins and thephoto-initiators. Heating was found to have a significant impact in thisstep. The phosphors are added third followed by mixing. In this case themixing is continued until the phosphors are well dispersed inside thesolution before adding a filler material. Phosphor materials havingparticle size distributions in the micron scale are best. The fillermaterials are added last. In the best mode the filler material isY₂O₃:Gd nano-particles and a fractional amount of Aerosil (or activesilica). Filler materials in the nanoscale particle size worked best. Itis of interest to note that in this case the Y₂O₃:Gd consists of 5 to 60nm particles and that the Aerosil material has fibrous like morphology.It is also of interest to note that the Y₂O₃:Gd particles canagglomerate and could form micron level aggregates. The resolution aswhat these aggregates could help is not clear.

The original intent was to determine the proper UV response and theadhesion between substrates at room temperature and with no other UVlight source except from the conversion of X-ray into UV. However, themixing of raw materials was performed with the fluorescent room lighton. It was discovered that the elapsed time under room fluorescent lightinfluenced the outcome of the cure extent. In essence, the UV light fromthe room assisted in photo-initiating the chemical reaction. The longerthe elapsed time for mixing under uncontrolled light, the more cureextent was achieved under X-ray energy. A controlled photo-catalysisinitiation was performed to take advantage of this discovery. This wascalled flashing the material with a UV light prior to curing underX-ray.

The initiation of the photo-catalytic reactions in adhesive materialswas achieved through UV-flashing by the following sequence in thepreparation. The raw materials were prepared under controlled lightonly. The photo-catalysis initiation was performed using a set timeexposure to UV light soon after the dispensing/application of theadhesive or during the dispensing/application of the adhesive prior tothe placement of the top substrate. The sandwiched part was then placedunder X-ray energy and cured farther. The materials that were subjectedto flashing cured faster than those that were not subjected to flashing.Based on cure hardness the flashing of select chemistries was done inless than (7.5 min) while the same select chemistries took longer (12.5minutes) when no flashing was applied.

The flashing is further exemplified in the following FIGS. 26A-C. A handheld or automatic piston pump dispenser 70 was used in this case. Theadhesive bead 60 was dispensed on substrate element 72 illustrated inFIG. 26A. The substrate in this case was polycarbonate. However it canbe appreciated that the inventive method is applicable to othersubstrate materials including composites and PET among others. Thedispenser applied the bead using a needle gauge 22. No phosphorsegregation was observable using a piston pump of the appropriate gauge.FIG. 26B, the bottom substrate 72 had a spacer element 74 made of Kaptonand having a thickness of 90 microns.

A UV source 73 was used to apply energy from within UVA range centeredaround 365 nm see FIG. 27. After 15 seconds to 25 seconds of UVAexposure another substrate element 72″ was applied on top. The assemblyhence formed was taken to the X-ray system for curing. It is recognizedthat the UV flashing can be done for longer times as needed; however,there a practical limitation to UV flashing.

Combining a UV light with the dispensing step is possible (FIG. 28). Byadding at least one UV light source to an automatic dispenser and byadding the necessary control logic 75 to turn on the UV light in acontrolled manner (UV intensity and UV elapsed time) at the end-of orduring the adhesive dispense, this UV flashing can be easily be scaledto high volume manufacturing.

The UV flashing is an effective method that allows the reaction to beboosted from a cost effective source. Subsequently to the flashing andalmost immediately, the substrates to be joined need to be placedagainst one another. The adhesive bead is then placed inside an X-raysystem. The X-ray energy can effectively complete the reaction of anadhesive bead that is inside a no line of sight region of an assembly.

The ability to dispense and flash the adhesive can be done with a highdegree of repeatability using an automatic dispenser having a mechanicaldrive consisting of a servo motor or a cable drive. In this case therobotic system is equipped with mechanical coupling mechanisms (orarticulations) 78 and a mechanical arm 77 to enable the placement of theadhesive dispense needle in a precise manner over a large area. Themechanical system further comprises a drive system 76 based on a servomotor or simply a cable drive.

The system can further comprise a platen 79 that is equipped with vacuumports 79′ and a source of heat 79″ such as a thermode (refer to FIG.29). The vacuum helps secure the substrates in place. The thermodeincreases temperature of the substrate. Adhesives at slightly elevatedtemperature can flow much more readily than at room temperature. Theviscosity of adhesives is typically lowered at elevated temperaturesuntil curing starts taking place in which case the viscosity startsincreasing, their viscosity, this is beneficial in specific applicationsbut not others. Some applications require the wicking of adhesivesthrough capillary forces underneath substrates or into porous materials.

In most applications the adhesion is promoted by having elevating thetemperature. To avoid running into the coefficient of thermal expansionmismatch between two substrates, the upper most temperature to which thesubstrate can be heated should be below its glass transition temperature(Tg). Below Tg the substrate expands at one coefficient of thermalexpansion and above its Tg the substrate's at a higher coefficient ofthermal expansion. As long as the temperature remains below Tg theadhesion could be promoted.

The UV flashing is accompanied by the curing of the outer layer (or theformation of a skin). This outer layer or skin reaches higher cureextent than the inside portion of the bead. Upon the formation of thisskin, the bead becomes unpractical because of the hardened outer layerbecomes an impediment to the controlled placement of the top substrate.The formation of an adhesive bond line through the juxtaposition of 2substrates becomes hard to do.

In other examples, the steps described above were repeated without anyUV flashing. So that the adhesive bead was prepared under controlledlight inside the fume-hood and kept shielded from light exposure untilwe exposed to the adhesive bead to X-ray energy. In this case theadhesive curing was conducted for 12.5 minutes to reach adequatemechanical bonding.

The flashing can be beneficial for other applications described in thefollowing example and illustrated in FIGS. 30A-D. A screen printer canbe used instead of an adhesive dispenser. The substrate element 72 ispositioned under the screen 90. A screen aperture 90′ can be positionedabove the substrate 72 but not contacting it. A blade 91 is passed withan adequate pressure to force the adhesive through the screen aperture.The screen is subsequently removed. The dispensed adhesive 60′ isexposed to UV energy for a controlled time (between 15 and 25 seconds).The top substrate is then positioned on top of the adhesive. Thesandwiched bead can be cured in X-ray for 7.5 min and successfully bondthe 2 substrates.

In one case the substrate was cross-ply carbon composite 80 in FIG.31A-C. The adhesive 60 was applied to the adhesive. Subsequently acomponent made of PET 81 was placed on the uncured adhesive bead. Theassembly hence formed was turned around and placed under an X-ray sourcefor curing. No flashing was used in this case. The adhesive bead curedin 15 minutes.

The X-ray curing system can have an additional source of radiation,namely UV. The UV radiation from the UV source 73 can be used inconjunction with the X-ray radiation from X-ray source 82. This enablesthe cure of adhesive beads that have a portion that is exposed to theoutside world and a portion that has no line of sight. An example isdescribed in FIG. 32 where a fillet 60″ has direct line of sight and canbe cured using radiation.

The fillet 60″ plays in an important role in flip chip applicationswhere stresses are maximal at the corner of the IC chips. The curing ofthe fillet 60″ can be done using an adequate recipe to minimizestresses. This would imply that the curing using UV radiation can bedone simultaneously, before or after the X_Ray radiation whicheverminimizes the inherent stresses.

In some cases dispensing 2 adhesive beads can be desirable. A dispenser70 contains adhesive 60 while dispenser 70″ contains adhesive 61. The 2beads are dispensed sequentially. A novel adhesive applicator isconceived. The novel dispenser 64 has 2 chambers and 2 coaxial needlesas illustrated in FIG. 33A-C. The inside container 62 contains adhesive61 while the external container 63 contains adhesive 63. Furthermore,the novel dispenser has a coaxial needle containing needle 64′ and 64″through which adhesives 61 and 60 flow respectively.

The adhesives were applied to the substrates using various methods fromsimple to more complex. In the simplest form the adhesive formulationswere scooped from the mixing cup using a spatula and deposited on thetop surface of one substrate. In other cases the adhesives were placedin syringes and hand pressed through a needle with an 18 to 22 gauge. Inother cases the materials were dispensed through the needle of EDF airpiston pump (also using 18 to 22 gauge needles). In some cases thesubstrates had a spacer element sandwiched between the substrates tokeep the materials from being squeezed out from between the substrates.The adhesive cure was demonstrated for adhesive bead thicknesses from 60microns to 1000 microns.

184 Resin 2100 Weight percent in percent in percent in Ratio of Phosphor% Phosphor Cure Adhesive adhesive adhesive Adhesive % by Weight TypeHardness Around 100 microns 0.94 0.02 0.04 0.75 0.25 CaWO₄ Yes BetweenGlass Slides 0.94 0.02 0.04 0.6 0.4 CaWO₄ Yes 0.88 0.04 0.08 0.75 0.25CaWO₄ Yes Around 250 microns 0.94 0.02 0.04 0.75 0.25 CaWO₄ No BetweenGlass Slides 0.94 0.02 0.04 0.6 0.4 CaWO₄ No 0.88 0.04 0.08 0.75 0.25CaWO₄ Yes

In some cases this was achieved using a polyimide film, while in othercases the spacer elements were glass beads. The curing of the adhesivethickness of the adhesive beads was successfully demonstrated at 60microns to 250 microns. These thicknesses represent adhesive beads thatwould be compatible with applications such as B-staged films and chip onboard applications. In other cases the adhesive bead was between 500microns to 1000 microns. These thicknesses represent adhesive beads thatwould be compatible with applications such as hermetic sealingapplications.

The control over the rheology and thickness of the adhesive beads wasachieved using filler elements such as AEROSIL and nanoparticles ofdoped Y₂O₃. Gadolinium was found to be the preferred doping elements inthese cases. In order to achieve thicknesses of 500 microns and abovethe adhesive formulations had between 0.5% and 5% of filler.

In some cases, the adhesive bead was applied between 2 polycarbonatesubstrates and kept in this configuration for 24 hours. No-flow ordisplacement was observable. The adhesive bead was therefore made toprovide the end-user with enough work and pot life after dispense and totolerate interruptions of the work in process during manufacturing. Thisis significant because no scarping of the work in process after dispenseis required.

Formulations 1 2 3 4 5 6 Resin 5 5 5 5 — — Resin (shadow cure) — — — — 55 Pl (369) 1.3 1.3 1.3 1.3 — — Pl (2959) — — — — 0.5 0.5 LaOB:Tm 1.5 2.53.5 2.5 2.5 2.5 Y₂O₃ — — — 0.3 — — AEROSIL 0.2 0.2 0.2 0.2 0.2 0.2CABOSIL — — — — — — MEKP — — — 0 0.1 —

It was found that recipe number 2, 3 and 4 cured faster than otherformulations. However adhesion was compromised when excessphoto-initiator was used. For this reason recipe 4 worked best. It curedfaster that recipe 2 and had better adhesion than recipe 3.

It was discovered that the uniformity of dispersion can be important tothe process. The more uniform the dispersion the better results in termsof adhesion. When clusters of phosphor rich and or phosphor poor areaswere noticeable, the cure was localized and the overall adhesion over asurface area was not good. When the photo-initiator is saturating themix (excessive amount of photoinitiator), the adhesion at surfaces iscompromised as there is a migration of un-reacted photo-initiator at thesurfaces.

Materials Information.

The first substrate is positioned in place. The location of thesubstrate and the mechanical registration is recorded. The adhesive isthen applied to the first substrate. The adhesive may contain a contrastagent to resolute a bead pattern on top of the first substrate. In suchcase a first substrate that is black should not have an adhesive colorthat is black. A white or off-white colored bead would be more suitable.A whitening agent like TiO₂ can be used as the contrasting agent. Inthis case the color of the substrate is irrelevant, since the inspectioncan be performed using X-ray radiation, the inspection of the bead cansimply be done regardless of the visible color contrast.

The second substrate is then positioned in place on top of the adhesivebead and the first substrate. The assembly is transported under theX-ray system that would perform a combination of X-ray based stepsnamely inspection and cure or one step consisting of curing. The X-raysystem comprises various elements that can be automated to satisfymanufacturing requirements. FIG. 34 illustrates some of these elementsthat form the X-ray curing system intended by the invention.

The step of X-ray radiation is preferably done in an enclosure 83 thatstops the radiation from leaking to the outside world. The enclosure 83can be made of various materials that include heavy metals such as lead.A single assembly 72′ can be held static or can be moved during cureinside the enclosure. Such movement could include a rotation movementthat can be achieved using a turn table. Such movement could alsoinclude a translational movement that can be achieved using an externalconveyor belt 85 and an internal conveyor 85′. Both the internal and theexternal conveyor belts work in synch to shuttle parts in and out of theX-ray enclosure. The door 84 can open up and close down to shuttleassemblies 72′ in and out of the X-ray radiation chamber. When the dooris open (or up position) the X-ray energy is off to adhere to safetymeasures. The X-ray enclosure can have automated doors with sensorslinked to a controller 76′. The enclosure can have doors that open upand down to shuttle at least one assembly in and out of the X-rayenclosure for irradiation leading to curing. Furthermore, the assemblyto be cured can be positioned inside a process fixture 86. The processfixture carries with it the assemblies 72′.

More than one assembly can be placed inside the X-ray machine. Theconfiguration having multiple assemblies can vary to maximize theloading of parts inside the X-ray curing system. As illustrated in FIGS.35A and 35B, 2 conveyors are juxtaposed one next to the other toincrease the packing factor (number of assemblies) inside the X-raysystem within plane. Because of the depth of penetration at the correctlevels, conveyors can be disposed within planes (FIG. 35A) and acrossplanes (FIG. 35B) inside the X-ray curing system.

An additional advantage of X-ray curing resides in its ability to curevarious size adhesive beads residing within different products using thesame curing parameters. As an alternative embodiment, the X-ray machinecan have more than one source, permitting curing of different assembliesat the same time (see FIG. 36). This presents an advantage and enablesthe manufacturer to cure different product mix inside the X-ray curingsystem. Assemblies 160 and 160′ can be cured at the same time. Thismeans that a product change over is easier and that the system isflexible in meeting cure requirements.

X-ray systems with the capability of programming recipes includingpulsing up to 30 times per sec can be done. A level of control over thekvp as well as amperage can be done to exert control over output poweras well as photon energy which in turns means control over depth ofpenetration.

Additionally, curing time and efficiency can be adjusted as desired byadjustment of various parameters, including, but not limited to,temperature, radiation source intensity, distance of the radiationsource from the adhesive composition to be cured, and photon fluxgenerated by the radiation source.

X-ray delivery head is on one side of the assembly, either above theadhesive bead or below the adhesive bead which can be described (thoughnot exact) that the adhesive bead is generally perpendicular to thedirection of propagation. In some cases the adhesive bead is generallyparallel to the X-ray radiation path. It is recognized however that theX-ray radiation is emitted in a flood beam have multiple directionsaround one predominant direction of propagation.

Metals and metallic coatings limit the penetration of X-ray radiation.For this reason, X-rays need to be oriented appropriately when curingintegrated circuits having metallic traces and coatings. In these casescenarios the preferred orientation of the bead is parallel to the X-raydirection of propagation. As illustrated in FIGS. 37A-C, twoconfigurations are possible. In one case FIG. 37A, the assemblies areoriented vertically to achieve the preferred orientation, in the othercase FIG. 37B, the X-ray source(s) is mounted in the appropriatedorientation to achieve the desirable alignment between bead anddirection of propagation. FIG. 37C provides a different view of thealignment between assembly 160 and the X-ray.

Wafer Bonding

After the wafer alignment is completed (using the method described inFIGS. 24A and 24B), the wafers are clamped together using a clampingfixture 88. The clamping fixture allows the wafers to remain alignedduring transport. The clamping fixture contacts the wafers on the waferback side with a depth typically within the exclusion zone of thewafers. The wafers can be placed on a rotating table 89 with a rotatingarm 87 as illustrated in FIG. 38A and FIG. 38B. The rotating table iscapable of taking withstanding pressure up to 40 kN. The pressure can beapplied using 2 mirror image rotating tables. The clamping fixture 88can be removed once the 2 rotating table have been engaged.

Since X-ray curing is done at room temperature or done at below theglass transition of the polymers used for bonding, not much pressure isrequired after the placement of the wafers on top of one another.Similarly, when a die is placed on a wafer surface, not much pressure isrequired.

The die on wafer application could use the same wafer set up describedin FIG. 39. However in the die on wafer bonding application the X-ray isaligned at an angle which leads to more depth of penetration over thearea array of the ICs 40′ disposed on top of the bottom wafer 41. Theplane of the bond line in this case is at 45 degrees vis-à-vis thedirection of propagation of the X-ray.

Safe Designs of X-Ray Systems (See FIGS. 40A-C)

Contact-Less Design for Clean Rooms (See FIGS. 41-42)

Containers that can be raised up and down to gate the assemblies 160that enters the processing chamber. Part of the cavity 90′ can be raisedto enable batching of assemblies 160.

Chamber 120 is fixed in place. The bottom of the cavity of chamber 122can be raised up and down to enable positioning wafers 41 that enter theprocessing station. The movable bottom does not touch the upperprocessing chamber (no contact between 120 and 122.

Bonding Fasteners on Composites (See FIGS. 43A-B)

A composite panel 80 is dispensed with adhesive 60. The metallicfastener 110 is placed on top of the substrate 80 using a pick and placesystem that is pneumatically driven (112). Both the pick and place 112and the adhesive dispenser 111 are mounted on KUKA robot 113. The X-raysources 82 are placed at a slight angle to couple to the bottom of thebolt 110.

More Specific Applications:

The following figures show various applications in semiconductorspertaining to packaging and encapsulation. These include: glob top, damand fill, molding (PMC, insertion molding) and flip chip underfill.

Underfill Under a Flip Chip:

An IC 28 is soldered in place in such manner that bumps 32 enter intoelectrical contacts with electrical pads 132. A desirable adhesive 60-1is applied by dispensing system 70 (see FIG. 44). If the substrate isheated to 20° C. above room temperature the adhesive wicks under thechip by virtue of the capillary forces set between the chip and thesubstrate 72. Once the adhesive is dispensed and wicked under the IC,the adhesive is ready for curing and optionally an inspection isperformed prior to curing. The standard method is to inspect theadhesive using optical means. However, since the adhesive 60-1 is loadedwith phosphors that have absorption characteristics in the X-ray regime,the inspection can be performed using X-ray radiation. The inspectionusing X-ray can reveal any striations that may exist under the IC 28.The uniformity of the adhesive can be determined to see if the adhesivehas separated into resin rich or resin poor regions. The adhesive can besubsequently cured with X-ray.

The curing in this case can be done at room temperature and the X-ray isbest coupled from the lateral side of the IC. In this case the directionof propagation is parallel to the plane of the adhesive bead.

Underfill for a High Density Circuit

A similar process can be applied if the substrate is a high densitycircuit (72″). Once the assembly is formed, the assembly can be placedon the mother board of a PC or a server using solder bumps (32′). Thisprocess is similar to the one used for mounting logic assemblies (e.g.;micro-processors and high density interconnect devices). FIG. 45illustrates the various elements.

No Flow Underfill:

To avoid the combination of time delay that takes place during adhesivewicking and the soldering process to connect the IC (28) onto substrate(72′), an encapsulant (60-2) can be dispensed on top of a substrate(72′) above the area array of contact pads (132). See FIG. 46. Anoptical inspection is performed. A chip is picked using a programmable“Pick & Place” (130) having provisions for vacuum (131). An activealignment is performed before the chip is placed onto a PCB (72′) insuch manner that the IC bumps (32) enter into electrical contacts withPCB electrical pads (132). The no-flow adhesive can be inspected andcured using X-ray.

Glob Top Application:

The glob top applications comprise dispensing an electronic polymer ontop of an IC (28) that has been die attached onto a PCB (72′) and wirebonded to establish electrical contacts between the active area of IC(28) and the electrical pads (132) disposed on the PCB board (72′) SeeFIG. 47. The special adhesive (60-3) containing the appropriatephosphors and photo-initiators can be applied to the IC (28) and enoughtime is allowed for the electronic polymer to flow and to cover the IC(28) and wire bonds (132′). The assembly is then inspected using X-rayradiation and cured using an X-ray radiation treatment or recipe. TheX-ray treatment can consist of pulses of controllable durationappropriate to harden the adhesive without inducing any damage to theassembly.

Dam and Fill

In some applications it is advantageous to apply a dam (60-4) or thefirst adhesive bead and subsequently cure the first bead prior todispensing an encapsulant (60-1) containing the appropriate phosphorsand photo-initiators required for X-ray curing. The current technologyallows co-curing of both 60-1 and 60-4 using X-ray radiation. See FIG.48. The amount of phosphors loaded in formulation 60-4 can bedeliberately high to cure faster than 60-1.

Molding/Post Mold Curing

Another standardized way of applying the encapsulation is throughinjection molding. The resin is applied at the mold level. In this casethe IC (28) is attached to the substrate (72″) and then inserted into amold. The mold is then clamped at high pressure and a liquid resin athigh temperature is injected at high pressures to fill the spacesbetween the wire bonds (132′) and the IC (28) See FIG. 49. The injectionmolding step is then accompanied by an elongated heat treatment. Thepresent invention is enabled through the use of a low-viscosity resin(60-5) that contains the appropriate phosphors and photo-initiators.After the injection molding at low temperature is performed, the X-rayinspection and X-ray curing can take place. The benefits of using thepresent invention are various but the most pronounced benefit to releaseall the stresses that can be established post molding. This eliminatesmost thermal annealing steps required for stress release. These stressrelease steps can take up to 4 hours which increases the Work-In-Processand does not lead to favorable economics.

Lid Sealing for MEMS and Miroprocessors

Another application that pertains to semiconductors and MEMS is lidsealing See FIGS. 50A and 50B. In this application three differentadhesives can be used. The combination of 3 different adhesives can beused: 1—An adhesive bead (60), 2—an underfill adhesive (60-1), and3—thermal conductive adhesive (60-6) that connects IC 28 with a lid 133.For semiconductors the lid 133 is typically metallic. For MEMSapplications the lid 133′ could be glass.

Micro-BGA Fill Encapsulation

A micro-ball-grid-array can be encapsulated in much the same way thatwas described for the glob top encapsulation. The configuration of theassembly is different than a chip on board application but theencapsulation of the wire bonds 132′ remains the same. (see FIG. 51) Anappropriate encapsulation 60-3 with the proper viscosity is prepared tocontain the amount of photo-initiators and phosphors to cure underX-ray.

Tab Bonding:

Tape automatic bonding (TAB) technique can be enhanced by the currentapplication. TAB is used to electrically connect a flexible circuit 134with a semiconductor IC (28) see FIG. 52. The flexible circuit containselectrical pads 132. The encapsulant 60-3 can be disposed on the TABarea. The application of the encapsulant is then followed by X-rayinspection and cure.

MicroFluidics

The joining of plastic 140-a to plastic parts 140-b that has mirrorimage features can be used to build functional plastic containers thathouse fluids and that have usable fluidic channels that can channelfluids from one side of the container to the other. The 2 pieces ofplastics having mate-able features are joined together using a filmadhesive 60-7 to form piece 140 c. (illustrating a cross sectionalview). The film 60-7 has the proper resin and the proper phosphors andphoto-initiators. The plastic housing formed is illustrated as part 140d (top view). See FIG. 53.

The fluidic channels can be formed using multiple pieces of plastics.The cross section of a PET plastic is shown in 150. The PET has welljoints as shown by groves 100. The fluidic channels 102′ are alignedwith the fluidic channels 102 present on another plastic such as LiquidCrystal Polymer 150′ In turn the sub-assemblies hence formed can be usedto form fluidic devices. An example of such sub-assemblies is provided.Each part of the subassembly can have conduits and interlocking featuresto allow apertures to be aligned. The adhesive bead 60-3 is dispensedand allowed to cure using X-ray. See FIGS. 54A and 54B.

The subassemblies are collapsed controllably. The protruding features101 enter into the well joint 100. These features enable the obtainmentof a hermetic seal since a fluid (liquid of gas) has to travel throughthe split well that is formed when the protruding feature 101 is engagedinside the well joint 100. The travel distance increases and thehermetic seal is enhanced.

Yet another example includes when a flexible circuit 134 having contactpads 132. The flex 134 is TAB bonded to IC 150 using adhesive 60-3. TheIC 150 has a resistive heating network that can increase the temperaturearound fluidic channels or apertures 102. The fluidic channels 102 arealigned with apertures or fluidic channels 102′ that exist on plasticparts 145-d. The IC 150 is bonded using adhesive 60. The fluidicchannels 102′ connect with fluidic reservoirs 152. These reservoirs cancontain Ink or insulin. See FIGS. 55A and 55B. When the flex assembly iswrapped around the housing 145-d the adhesive film 60-7 is activated tobond the outer walls of 145 d with the flex 134.

The plastic joining does not have to use mirror image plastics nor doesit have to use similar materials. In fact dissimilar materials can beused to form plastic housing for insulin pumps or inkjet containers.

Formation of Ink Jet Cartridges

Ink jet cartridges are typically made of a plastic housing made of athermoplastic moldable resin, such as polyethylene terephthalate (PET),polyethylene, or polysulfone for example, as the base material.Polysulfone describes a family of thermoplastic polymers that havetoughness, mechanical stability and ink resistance.

Typically, a print head made of silicon, has numerous nozzles that areused as ink outlets. The nozzle array on the silicon and the inkreservoirs are connected through a manifold structure having fluidicchannels. The fluidic channels are employed to direct the inks ofdifferent colors from the primary reservoirs to appropriate printheadnozzle arrays.

Multicolor cartridges have a plurality of ink reservoirs, often threeink reservoirs. In such three ink cartridges, each of the reservoirscontains a primary color. These reservoirs need to be isolated from oneanother. The separation between the compartments has to be hermetic toavoid ink mixing between the various compartments. A plastic piece isadhesively bonded to seal the separate reservoirs.

The joint of interest that seals or separates the various reservoirsmust be made to withstand the prolonged contact with inks. Inks happento be aggressive from a chemical stand point. Furthermore, the sealingjoint needs to be able to overcome the mechanical stresses that mayexist over the product's functional life and the pressure differentialthat needs to be regulated between atmospheric pressure and the internalpressure in the reservoir.

The ink reservoirs and the ink channels, the plastic structures andmanifolds necessary to form the multicolor cartridge can be assembledfrom multiple injection molded plastic parts. The most economical way isto injection mold as one part all of these parts. However, the lid sealand the tri-chamber separation cannot be injection molded as a unitarybody, since it is required to have accessibility to the reservoirs.Regardless, whether the cartridge is formed from three pieces, or morethan three pieces, two process methods are typically used to bondplastics: Ultrasonic energy welding and thermally curable adhesives.

The problem with ultrasonic welding is that it does not work withdissimilar materials. The other method consists of using adhesivematerials to bond the various parts together. The various plastics partsin this case can be of similar or dissimilar materials provided theadhesive is subjected to enough thermal energy.

The application of thermal energy necessary to cure the adhesives leadsto thermal expansion of the plastic parts. The thermal expansionmismatch between different materials results in thermally inducedstresses locked at the interface of the various materials.

The print head is connected to a flexible circuit using a TAB bondingmethod. The print head rests on an adhesive bead that bonds the printhead to the manifold containing fluidic channels. The print headcontains nozzles that can be fired by the electrical signal that feed aresistive network built on the silicon. The electrical signals that areselectively applied to specific nozzles results in the heating of theselect nozzles and therefore leads to the controllable ejection orsquirting of ink droplets. The ink droplets are directed to the printmedia like paper to form patterns leading to words, images and the like.

The present invention adhesive composition can be used in the formationof inkjet cartridges, such as those described above or in formation ofinkjet cartridges according to the conventional art, such as U.S. Pat.Nos. 7,832,839; 7,547,098; or U.S. Pat. No. 7,815,300, for example, thecontents of each of which are hereby incorporated by reference.

Leaky Optical Fiber Element:

Fiber element 91 can be straight or can be flexible to adopt variousshapes. The fiber element leaks UV energy around its core and along thedirection of propagation of the UV light. When light is coupled from itsends the light propagate along the fiber and leaks UV lights to itsenvironment. (see FIGS. 56A and 56B)

The fiber element is inserted in a joint between 2 plastics. An adhesiveis dispensed around the fiber and the assemblies are collapsed together.The curing can therefore be achieved by coupling UV to the externalsides of the fiber element to distribute UV light to the inside of theassembly. (See FIGS. 57A and 57B)

UV Ink for Digital Printing Presses

The CaWO₄ phosphors and CaWO₄:Pb emits in the visible and UVA underx-ray energy. Both these phosphors have a notoriously slow decay time.This phosphor keeps on emitting visible and UV light even after theinitiating energy has stopped. The emission remains strong for 60 to 100seconds after x-ray energy irradiation has stopped.

For this reason, the CaWO₄ as well as the CaWO₄:Pb can be applied for adelayed curing application such as UV inks. The UV ink offers thepossibility of rapid cure under UV light. The inclusion of nano-particlesize phosphors that have light modulating capability from x-ray andextreme UV to a desirable UVA and visible range are particularlypreferred. The initiating radiation can flash (short burst exposure) theink and the included phosphors with delay decay time can keep onemitting UV radiation that can cure the ink.

These special inks can be used in digital presses equipped with EUV orx-ray sources to flash activate the phosphors with slow decay times. Theweb-speed can therefore be accelerated from 400 feet per minute to over900 feet per minute by virtue of the sustainable UV emissions that cankeep on curing the inks from within the thickness of the ink itself.

This is especially useful when using glossy paper. The glossy paperoffers limited porosity if any. For this reason, inks wetting thesurface remain in wet form and do not dry quickly. Thermal energy can beimparted to the surface of the web to assist in removing the solventsused in the inks. The solvents have a slow drying rates and cannot beeasily removed which slows down the web speed.

The combination of thermal energy and an initiation radiation can beused in the present invention.

A reel of glossy paper (200) feeds a portion of the digital printingpress described in FIG. 58. The paper is imparted with ink though an inkdispensing station (201). The source of an initiation radiation (202)flashes the ink with x-ray or EUV. The phosphors embedded within the inkand having a slow decay time are activated with the x-ray or EUV. Thepaper moves to the thermal station (203). The paper is then turnedaround a first pulley (204) and a second pulley (204). The back side ofthe paper is now ready for printing using a ink dispensing station(201). The thermal treatment as well as the UV flashing is imparted onthe ink using station 203 and 202. The paper is then moved to anotherportion of the digital printing press.

Various other embodiments are possible.

Composites:

The present invention adhesives can also be used in the formation ofcomposites, by the adhesion of two or more plies, which are thefundamental building blocks of layered composites. The composites can bebuilt by layering the plies, with the plies adhered one to the otherusing the adhesive composition of the present invention. Anyconventional ply can be prepared, such as −45+45 assemblies (See FIGS.59A and B), 0+90 composites (see FIGS. 60A and B).

The composite is preferably formed by preparation of a prepreg materialformed of the plurality of plies, with each ply placed in the desiredconfiguration with respect to the other plies, and having the curableadhesive composition of the present invention between respective layersof the plies. Once the prepreg is assembled, and the layers aligned asdesired, the curable adhesive can be cured by application of the desiredionizing radiation, such as X-rays, thereby adhering the plies togetherto form the composite.

Front End Semiconductor Photo-Lithography

The adhesive composition of the present invention can alternatively beused in photolithography as a curable resin to accomplish eithernegative or positive photo-resist development. By the use of heavy metalmasking elements, it is possible to get selective curing of the presentinvention composition to form desired patterns or semiconductorelements. If the element is desired to be electrically conductive, theadhesive composition can be doped with electroconductive fillers, asdesired.

Semiconductor Integrated Circuits (IC)

In the production of semiconductor integrated circuit (IC) devices, anIC device is often conductively attached to a substrate by the use ofsolder balls attached to the IC device, then the solder balls are placedon conductive electrical pads attached to the substrate. FIGS. 63A-Gprovide a representation of one use of the adhesive and conductive resincompositions of the present invention in a manner to replace the use ofsuch solder balls and solder masks while maintaining high electricalconductivity between the IC device and the electrical pads. In FIG. 63A,a semiconductor IC (300), such as those present in logic or memorydevices, system on chip or optoelectronic devices, particularly devicesbased on GaInNAs or GaAs, has a plurality of“bumps”, “pins” or “feet”otherwise referred to a protrusions (301) attached to one side of thesemiconductor IC (300), wherein the protrusions (301) are formed of anelectrically conductive curable resin, preferably an electricallyconductive curable resin containing metallic silver flakes and energyconverters of the present invention, most preferably an electricallyconductive curable epoxy containing metallic silver flakes and energyconverters of the present invention. The term protrusion in item (301)includes, but is not limited to, the above noted items 32: Flip ChipDevice Bumps, and 32′: Substrate Solder Bumps. The plurality ofprotrusions (301) can be applied to the semiconductor IC (300) throughany desired method. Preferably, the protrusions (301) can be applied byjetting, screen printing, electroplating or another means of dispensing,in order to place the protrusions (301) at the desired locations for theparticular device. The protrusions (301) can follow a desirable patternsuch as an area array or a perimeter array configuration to mention twoexamples.

The semiconductor IC (300) having the protrusions (301) is then aligned(FIG. 63B) and placed (FIG. 63C) on a substrate (302) having a pluralityof conductive electrical pads (303) in a pattern corresponding to thelocation of the protrusions (301) on the semiconductor IC (300). Oncethe placement has been completed, the conductive resin protrusions (301)are cured in place by the application of X-ray or e-beam energy throughthe semiconductor IC device (300) (FIG. 63D) (or alternatively throughthe substrate (302) (not shown), whereby the energy converters in theconductive resin protrusions (301) convert the x-ray or e-beam energyinto the initiation energy causing the conductive resin to cure andharden. In this construction, the substrate (302) may contain tracesthat are conductive in order to provide desired electrical connectionthrough the electrical pads (303), or the substrate (302) may benon-conductive. The 302 substrate can be a flexible or a rigid circuitboard. Furthermore, the rigid circuit board can be organic such as FR4and BT, or can be ceramic such as alumina (Al₂O₃) or doped alumina. Thecircuit board can be a multilayered circuit board containing at leasttwo layered with via to interconnect internal planes such as a powerplane or a ground plane. If the substrate (302) is non-conductive, theelectrical pads (303) may be connected through patterned electricalconnections from electrical pad (303) to electrical pad (303), ifdesired. This will be determined by the particular semiconductor ICassembly being prepared and is readily determined by one of ordinaryskill in the art. One advantage provided by use of the present inventioncurable resin/adhesive compositions is the ability to generate finelycontrolled and intricate patterning for electrical conductivity by theuse of conventional photolithography and similar techniques, while notrequiring line-of-sight access for curing of the resins involved.Alternatively, the protrusions (301) can be placed on the substrate(302) and subsequently an IC (300) is aligned and placed on top of thesubstrate (302). Yet another alternative is that the protrusions (301)may be disposed on both the IC (300) and the substrate (302), thenjoined during curing of the protrusions after the IC (300) and substrate(302) are aligned and placed together.

Once the conductive resin has been cured, a curable underfill adhesive(304) is applied via a dispenser (350), wherein the curable underfilladhesive (304) is an adhesive according to the present invention,containing one or more energy converters (see FIG. 63E). Preferably, theunderfill adhesive composition is a non-electrically conductive (orelectrically insulating composition) to isolate the conductive pathsformed by the protrusions (301) and electrical pads (303). Oncedispensed, the curable underfill adhesive (304) is cured by applicationof x-ray or e-beam energy through the semiconductor IC device (300)(FIG. 63F) (or alternatively through the substrate (302), not shown).

When a metallic heat sink is desired, the metallic heat sink layer (306)is applied to a side of the semiconductor IC device (300) opposite tothe protrusions (301), electrical pads (303), underfill layer (304) andsubstrate (302). Preferably, as shown in FIG. 63G, the metallic heatsink layer (306) is attached to the semiconductor IC device (300) by wayof an intermediate curable thermally conductive adhesive layer (305).Once the metallic heat sink layer (306) is aligned and placed on thecurable thermally conductive adhesive layer (305), the curable thermallyconductive adhesive layer (305) is cured by application of x-ray ore-beam energy, through the metallic heat sink layer (306) or through theunderlying semiconductor (300)-protrusion (301)-substrate (302)assembly. Alternatively, the X-Ray energy (or E-beam energy) can beapplied from the sides of the device (as is shown in FIGS. 37C, 38A and38B). A combination approach whereby the device is irradiated from allsides can also be envisaged.

The thermal conductivity of a curable adhesive or resin of the presentinvention can be enhanced by loading the resin with metallic particles(that are inherently thermally and electrically conductive).Alternatively, the resin can be doped with a metal nitride, such as AlN(aluminum nitride) and BN (boron nitride), for increasing thermalconductivity without necessarily increasing electrical conductivity.

Furthermore, the electrical conductivity of the resin can be increasedmuch more than thermal conductivity through the use of materials such asgraphene or other conductive carbon materials.

By way of example, a curable resin of the present invention containingx-ray to UV energy converting particles can be doped with silver, copperor graphene (as the electrically conductive material) and cured usingX-Ray energy. The metallic particles generate significant secondaryelectrons which can also assist in the cure cycle of the resin. This iscounter intuitive since UV resins normally need to beUV-transparent/clear to be cured by UV light. This is not the case forthe present invention curable resins, which merely need to be penetrableby X-Ray energy. The UV light is generated deep inside the bead ofadhesives and the metallic (or carbon) particles generate secondaryelectrons to enable/enhance free radical curing mechanisms to takeplace.

The thermal conductivity and the electrical conductivity of the presentinvention resins or adhesives can also be improved by doping them withmetallic particles and flakes (especially for Ag). Similarly, thethermal conductivity can be improved through the use of high thermalconductivity dopants in particle or platelet forms such as for metalnitrides such as AlN or BN.

As an alternative to the standalone metallic heat sink (306) of FIG.63G, it is also possible to have the semiconductor (300)-protrusion(301)-substrate (302) assembly hermetically sealed inside a cavityformed by the metallic heat sink layer (307), having support sides (308)(see FIG. 64), wherein the metallic heat sink layer (307) is attached byway of the same type thermally conductive adhesive resin (305), but inthis embodiment, the metallic heat sink layer (307) extends beyond theedges of the semiconductor (300)-protrusion (301)-substrate (302)assembly, and is supported at its ends by support sides (308). Whenthese support sides (308) completely surround the semiconductor(300)-protrusion (301)-substrate (302) assembly, the semiconductor(300)-protrusion (301)-substrate (302) assembly is hermetically sealed,and has a cavity between its edges and the inner surface of the supportsides (308). As in the standalone metallic heat sink (306), the metallicheat sink layer (307) of this embodiment is connected to thesemiconductor (300)-protrusion (301)-substrate (302) assembly via thethermally conductive adhesive resin (305), which is cured after themetallic heat sink layer (307) is aligned and put in place, byapplication of x-ray or e-beam energy through the metallic heat sinklayer (307). The resulting assembly is a packaged IC product or device.

In a further embodiment of the hermetically sealed assembly of FIG. 64,FIG. 65 shows a similar construction, except where the metallic heatsink layer (307) has had a section directly over the semiconductor(300)-protrusion (301)-substrate (302) assembly replaced with a window(309) that is transparent to a given wavelength of light, to enable theIC within the semiconductor (300)-protrusion (301)-substrate (302)assembly to receive and/or transmit the desired wavelengths. Such IC'scan be light emitting diodes, vertical-cavity surface-emitting lasers(VCSELs) or edge-emitting semiconductor lasers. In the case of thelatter, one or more of the support sides (308) can be replaced by asuitable window (310) (rather than having a window (309) in the metallicheat sink layer (307) (not shown), or in addition to the window (309) inthe metallic heat sink layer (307) (shown in FIG. 66)) that istransparent to the desired wavelengths emitted or received by theedge-emitting semiconductor laser.

Alternatively, the semiconductor (300)-protrusion (301)-substrate (302)assembly (with or without the underfill layer (304)) can be encapsulatedwithin a glob top (311), preferably one that has high opticaltransmissivity, as shown in FIG. 67. The glob top (311) can be formedfrom a direct UV cured adhesive or resin composition, a thermally curedadhesive or resin composition, or from an adhesive or resin compositionof the present invention having one or more energy converting materialscontained therein to permit x-ray or e-beam cure of the glob top (311).In the case of use of the adhesive or resin composition of the presentinvention in such configurations, since the glob top (311) desirably hashigh optical transmissivity, it is preferable to have the energyconverting materials contained within the curable adhesive or resin beof a particle size that is below the optical wavelengths that aredesired to be transmitted through the resin. Most preferably, theseenergy converting materials would have a particle size of 400 nm orless, in order to retain the desired optical transmissivity of the globtop (311). The glob top resin is X-Ray absorptive and can be madeoptically transparent by a careful selection of the size of the energyconverters.

In addition to the device embodiments described above, methods of makingthese devices as described above are also included within the presentinvention. Of particular advantage in these methods is that the x-ray ore-beam curing of the various types of curable resin/adhesivecompositions can be performed at room temperature in order to avoidproblems associated with different coefficients of thermal expansion ofthe materials forming the various components, and avoidance of thepotential heat damage of the often delicate and intricate circuitrypresent in the semiconductor ICs involved if thermal curing was used.

One of ordinary skill will readily understand that any of theseembodiments described herein can be combined in various permutations asdesired. Each of such permutations are likewise included within thescope of the present invention.

While many of the above described embodiments use downconvertingparticles that are dispersed throughout the curable adhesivecomposition, many other configurations are available for use with thepresent invention. For example, the downconverting particles can beadhered to a thin film (preferably to both sides of the thin film) whichcan be placed between two surfaces, each of which is coated with thecurable adhesive monomer and photoinitiator formulation. Uponirradiation, the downconverting particles emit energy at the desiredwavelength, activating the photoinitiator, and initiating curing of bothlayers of adhesive, thus bonding each of the surfaces to an oppositeside of the thin film having the downconverting particles. One ofordinary skill, upon reviewing the present invention, would readilyunderstand a wide variety of configurations that could be used to createnovel adhered structures.

EXAMPLES

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

The materials chemistries were prepared by first weighing the keychemical ingredients and mixing these chemical ingredients under heat. Afunctionalized Acrylate resin was obtained from BASF. The resin was madefrom a mixture of 4 commercially available products including Laromer LR9023, Laromer PO 94F, Laromer TPGDA, Laromer LR 9004.

The photoinitiators were also obtained from BASF and consisted ofIRGACURE 369 and IRGACURE 2529. The phosphors were obtained fromPhosphor Technologies. The LaOBr:Tb³⁺ phosphor as well as the YTaO₄ wereused in the preparation of the curing formulations. The third phosphorwas Y₂O₃ doped with Gadolinium (Y₂O₃:Gd). This third phosphor wassynthesized in nano-particle size. It was used both as a phosphor and asa thickening agent.

The temperature that was used during all the mixing steps was 80° C. Thesequence of adding the various chemicals was as follows: 1-resin,2-photoinitiator, 3-phosphor and 4-thickening agent. In one case thethickening agent was the Y₂O₃:Gd. The mixtures stirred every 10 minutesfor one hour to two hours. This ensured the obtainment of a homogenousmixture.

In one case MEKP was added to an adhesive formulation to assess theeffectiveness of X-Ray curing on coupling energy to MEKP and enhancingthe cure kinetics. It was found that recipe or formulation number 2, 3and 4 cured faster than other formulations. However adhesion wascompromised when excess photo-initiator was used. For this reason recipe4 worked best. It cured faster that recipe 2 and had better adhesionthan recipe 3.

It was discovered that the uniformity of dispersion was critical to theprocess. The more uniform the dispersion the better results in terms ofadhesion. When clusters of phosphor rich and or phosphor poor areas werenoticeable, the cure was localized and the overall adhesion over asurface area was not good. When the photo-initiator is saturating themix (excessive amount of photoinitiator), the adhesion at surfaces iscompromised as there was a migration of un-reacted photo-initiator atthe surfaces.

Curing of the various formulations was done on PET, glass,polycarbonate, polyimide, polysulfone, a carbon prepreg, a FR4 PCB. Theadhesive bead was sandwiched between two similar substrates and curedwhile in between the substrates. No temperature was increased while inthe x-ray. The temperature was measured using a hand-held IRthermometer. The only time a noticeable temperature increase of up to10° C. was observed is in the case of the formulation containing MEKP.

Formulations 1 2 3 4 5 6 Resin 5 5 5 5 — — Resin (shadow cure) — — — — 55 IRGACURE (369) 1.3 1.3 1.3 1.3 — — IRGACURE (2959) — — — — 0.5 0.5LaOBr:Tb 1.5 2.5 3.5 2.5 2.5 2.5 Y₂O₃ — — — 0.3 — — AEROSIL 0.2 0.2 0.20.2 0.2 0.2 CABOS1L — — — — — — MEKP — — — 0 0.1 —

Additional formulations were cured. The elapsed time under X-Ray was 10min, 12.5 min, 15 min, 17.5 min and 20 min. The formulations that weremade using the LaOBr:Tb³⁺ phosphor cured between 10 min and 12.5 min.The formulations that were made using the phosphor YTaO₄ cured between12.5 min and 15 min. The formulations using the third phosphor was Y₂O₃doped with Gadolinium (Y₂O₃:Gd) cured in 17.5 minutes. However when theLaOBr:Tb³⁺ mixed with Y₂O₃:Gd were added to the adhesive formulations,the cure was accomplished in 10 min.

Formulations 1 2 3 4 5 6 Resin 1 6 6 6 6 6 6 Resin 2 (shadow Cure) 0 0 00 0 0 Pl (369) 0.6 0.6 0.6 0.6 0.6 0.6 LaOBr:Tb 1.5 1.5 Y₂O₃ - Ian 1.51.5 YTaO₄ 1.5 1.5 AEROSIL 0.3 0.3 0.3 0.3 0.3 0.3

Obviously, additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. An electrically conductive resin or adhesive composition comprising:an organic vehicle comprising at least one polymerizable monomer which,upon polymerization, forms an electrically conductive resin or adhesive;at least one photo-initiator responsive to a selected wavelength oflight; and, at least one energy converting material selected to emitsaid wavelength of light when exposed to a selected imparted radiation,such that the resin or adhesive composition formed exhibits electricalconductivity or semiconductivity without the presence of an electricallyconductive additive, wherein the electrically conductive resin oradhesive composition formed comprises at least one member selected fromthe group consisting of poly(fluorene)s, polyphenylenes, polypyrenes,polyazulenes, polynaphthalenes, poly(pyrrole)s (PPY), polycarbazoles,polyindoles, polyazepines, polyanilines (PANI), poly(thiophene)s (PT),poly(3,4-ethylenedioxythiophene)s (PEDOT), poly(p-phenylene sulfide)s(PPS), poly(acetylene)s (PAC), poly(p-phenylene vinylene)s (PPV).